Here are three companies that sell them, I'm sure there are more. You might also want to see if you have local nurseries that sell them, though it might be getting late in the season for them to have much stock.

https://rootstofruitsnursery.com/collections/apple-trees?srsltid=AfmBOopdELJ8Y7GdAxmby0HRFbS1qmW5wRSDQ_mhlhOofzGs3ZVt-6wB

https://skipleyfarm.com/nursery-plants-blueberries-apple-trees-fruit-trees/grafted-trees-apple-cherry-plum/

https://www.willisorchards.com/category/fruit-trees?srsltid=AfmBOopoflaywO2Pp_oDcUrf-jtAJzI4tC7VvQs4x8rktLqtjw2dWe-e

And I know this company has good stock, though again, might be too late in the season to order:

https://www.grandpasorchard.com/Tree-Type/Apple-All-Varieties

From the viewpoint of a backyard grower and not a commercial grower, I don't completely agree that advice. In my experience, it has been much easier to establish trees that are bit older, mainly because they can withstand insect pressure better and because you're starting out with a larger tree that gets above browsing height quicker, you don't have to work for as many years to keep the deer off of them. Think in terms of size you'd buy potted locally, which is what I prefer to do if possible. Problem is, variety is limited locally, so I've had to resort to mail order for many of my trees.

Trees of Antiquity is excellent, and Raintree Nursery is pretty good. I've ordered once from

Grandpa's Orchard and received an excellent tree, so I'll put in a plug for Grandpa's, too.

I've been very happy with the bare root stock from Fedco in Maine. Many varieties available including lots of heritage varieties, most on a choice of several different rootstocks. They won't ship until spring of course.

I don't disagree that bigger trees can be easier, I'm not sure that time to maturity is very different. I have to put them in wire cages to survive my herd of deer.

Thanks for your helpful responses, beesneeds, porkchop_z5b_MI, and rwiegand. 🙂

So I guess the advice about strictly planting one-year-old apple trees isn't necessarily gospel, which at least makes things more flexible. Yeah, after learning the hard way, I too have to put out wire cages to protect small trees from those erratic deer. 😏

I appreciate all the nursery suggestions, and I will check out the links!