I want bunch grapes too, and the fellow at Isons probably knows his stuff about bunch grapes.
We have someone a few blocks from us who planted what I think is a Mars or a Concord (it was supposed to be white, but it wasn't). It has been doing fine. She's got it on chain link and it does not get disease - this is year three.
The grapes are not large, have seeds but are tasty enough for juice or jam. However, they are not what I grew up with as Ontario style table grapes, I think that one might be impossible here. I don't much like the muscadine or scuppernog.

Thank you. I have plans for muscadines as well. I'm doing a 24'x16' arbor to put six varieties on. My thing on muscadines is that back home a muscadine was the wild vine that us kids would go to the woods and shake to get to the grapes. The ones folks would grow on an arbor were always bronze and called scuppernongs, irregardless of variety.
My tastes run towards to the wild muscadines and I have have been assured that the Ison variety has that wild flavor.
BTW, I'm the same way on blackberries much prefering the wild taste to most of the domesticated cultivars.

I have himrod and reliance on my back deck. I am about 18 months in. I had a couple of runs this year, and the reliance produced 2 bunches, the himrod produced 5, but the reliance actually came 100% to fruition, while the himrod (which got fleeced by a caterpillar while we were in Germany and France for a week) only managed to get half a dozen berries out of those clusters to actually be edible. The squirrels and birds enjoyed the rest.

I am growing both in pots that are approximately 12"x12"x12". Neither are supposed to have a seed, yet some clearly had 2-3 small pits, and the skin was a bit tough. They were a bit smallish in size. I am guessing this is because this is the first fruiting year and I haven't read any books on how to prune.

I believe that reliance is the suggested alternative to concord here in GA. I recall hearing one of my two varieties is. I am also looking to build a pergola on our 2nd story deck, and use much larger/deeper planters to plant grapes.

I am very new to this, and the vines are new also - bought as a pair of sticks in a cardboard box @ a big box hardware store. So....take or leave it. I didn't go to Ison's or others, although I highly considered it. I might in the future, if these vines get something nasty and die.

What nobody will tell you is that you'll be lucky to get a "bunch" like you will see in a store. Here is one of my Reliance bunches just days before we picked (early August)

Update

It turns out that what I was looking for is right under my nose. I was doing a little cleanup yesterday and found that I do have a bunch grape on the place already. I bought this place this past spring and have had time only to throw in the garden. I have lots of work to do on the place that is waiting for cooler weather, including a massive bamboo removal job.
I was clearing a small area in the corner of my chain link fence and found a small grape vine. At first I thought muscadine due to the leaves but they weren't quite right for a muscadine (round and toothed like a muscadine but with a pronounced point rather than being nearly round) the clincher was forked tendrils. I have no clue as to variety but do know that it is at least three years old as the previous owners were only here for two years and I serious doubt they had anything to do with grapes other than the bottled version. Judging from the main vine at the base it is even older than that being over an inch in diameter and appearing to have survived multiple attacks of the weedeater. All canes were small being pencil sized with short nodes. It is also in a terrible location being in a corner on a boundary fence behind a crepe myrtle (those will be going along with the bamboo).
I guess I need to develop a mangment plan for it with some TLC and we'll see what I got.

Good luck!

Moreover, good luck with the bamboo and crepe myrtle removal. If you don't get the myrtle out along with all the roots, just like holly trees, it will keep coming back. I have no suggestion on the bamboo removal except KILL IT WITH FIRE! ;)

Bamboo control has commenced. I need to remove a 15x30 area to get my trellis in. I am running the trellis down thw full length of my garden 120'. My vegetable garden is 120'x 75' and can stand to be shrunk just a little. I also laid out my asparagus beds and plotted out where to put the strawberries. I will be losing 10' on the western and northern sides of the garden.
Anyone else with knowledge of bunch grapes in Atlanta?

I have only limited proof (3 years). I purchased Mars and Venus from Johnsonnursery.com (based in Elijay, Ga). The Vines have done well with no sign of Pierce's disease. They reportedly have disease resistance to mildew and do well with higher humidity, and I grossly over-interpret that to mean they are generally healthier. I had a nice crop this year, but I travel, and as they were finally ripening something got'em (probably racoons). I listen to Walter Reeves on the radio saturday morning, and he is always repeating to stay away from concords, but I don't have any personal experience. I'll be interested to read responses from people with more experience, but that is exactly what the extension agents are. Perhaps we are all optimists. Good luck with the Bamboo! You may want to ask about Pierce's disease on the orchard forum.