I agree w/mnvikes, rakgrape is a good source. If you want free, next winter put in an order to the germoplasm. Raintree is good also, you just really have to demand that you want your plants before they want to ship them for your area normally.
Example, every year I like to get my dormant plants in the first week of April. We still get a snow storm or two, but the plants arrive dormant so it's no big deal, they get tucked into their new homes and wake up as they should. On the other hand, if your plants show up in late May or even June, it's already hot and they have broken bud and are under stress from the get go.
For me, this results in a massive difference in the first years growth; which determines if they survive the following winter as well. In short, if you want to start grapes this year, you need to get an order in pronto.