Contact the landscape arboretum in Chaska. They keep libraries of nurseries in and around our area. IIRC the fruit and tree nursery had a hand in developing this variety.

You should be able to order La Crescent grapes from Jungs in Randolph, Wisconsin, next spring. Google La Crescent grapes for additional sources.

Or check with Bachman's or Minnesota Valley, Gertens or Minnehaha Falls Nursery. It is probably too late to even find any potted stock this year, but even if they do not plan to carry open stock next spring, they may be willing to special order it for you. Almost certainly Baileys will have this variety available to its wholesale customers, which will almost certainly include all of those I named. How many of them will do this kind of special order I do not know. Nor do I know the quantities you may have to take.