Never heard of it, you might try contacting the wineries directly. Maybe its like Starbucks & coffee grounds & given out on a first come first served basis.

If it is good the the grape growers will grab it before anybody else. Nowadays they press grape seeds and get the oil and sell it. But still the pulp should be a good soil amendment.

Compost is good, but exotic composts such as Grape Seed Compost seldom meet the expectations those selling it promote. I would not expend much time and energy looking for some and would not spend my money buying any.
Compost should be a mix of many things.

Winery leftovers, the "pomace", are high-value. Traditionally it's spread back onto the vineyards and tilled in at small operations.

it's good cattle feed, and some separate the pomace into grapeseed oil, polyphenol extracts from the skins, make biodiesel fuel and the residue from all this can be composted and used as compost or potting soil.

One thing about compost, generally speaking various materials will end up in about the same place when fully decomposed. There are some differences of course, which is why the rule of thumb is 'vary the ingredients', but within reason, most materials will move toward a common center. Good basic compost, and plenty of it, will do more for your garden than chasing after specific exotic products.

Which is not really what the OP asked, and I don't mean to rain on your parade. It's a free country, so if you can find it, go to it.

The best compost is the compost you make yourself, recycling all your nutrients in your garden. I'm with the rest of the people who say save your money, I wouldn't buy it. You can't buy good soil, you have to make it. Soil coming from a dumb trunk probably isn't going to have a healthy food web, you have create that foodweb(organic matter, compost, mulch,etc).

When I first started out, I shoveled truckfuls of free compost from the city. This compost doesn't have a complete foodweb, or any of that jazz. But, I'm sure it has something, if anything just the organic matter.. There was no noticeable difference between the free compost i got from the city and the compost $40 a yard at the nursery. At least that is what my wallets telling me, my back is saying quite the contrary, I had to shovel the free compost from the city manually.

My goal in composting is not to make fertilizer, but organic matter, for soil amendment. I am sure things like leaves and grass clipping are more than just "N"itrogen source. For example, "K" and "P" and calcium are going to stick around no matter how you compost : Cold, Hot, Fermentation .. And perhaps there are a lot more trace elements there. I can buy 21-0-0 fertilizer for less than $1/lb,

JMO

As mentioned, grape pomace is returned to the soil in many vineyards. In areas with a special disease problem the grape seeds are composted first as a means to kill a virus. The disease is unusual by being infective via seeds. If I recall correctly, the composing was to germinate the seed and then kill the sprout, and then decay it a bit. It sounded as if the composting heating aspect was not the main control.

high phosphorus of course, and high N, and acidic. Ideal for Michigan low P, alkaline soils. I used it until I stopped making wine. Lots of germination since I did not hot compost.

Amazon has a book that mentions it. $150. Free shipping.

American Soil & Stone has this on its website:

Super Grape Compost

Made from composted grape pressings. Last season's grape harvest is this year's Super Grape Compost! Super Grape is OMRI listed as Harvest Compost. An extremely nutrient rich compost great for topdressing to improve fertility or blend with existing soil to increase the organic matter content and fertility. An excellent source of nitrogen. Can be used as a topdress placed at a depth of ¼-½ inch. Incorporate into soil at approximately 25% by volume. Upper Valley Recycling is the producer of Harvest Compost.
Contains: Composted Grape Pressings (Pomace)

No info on nutrient content. I checked Upper Valley and their website has no info on nutrients either as far as I can tell. So, difficult to make any judgments on its 'quality'. But I stand by my earlier post and many others in the thread saying that it's probably great, but probably not worth a premium price.