I ordered fruit trees from Stark early this spring, and had the same trouble with their online ordering. I called the company, spoke to a delightful woman named Carla, got my order processed and she told me of "daily specials", one of which was a grape I had been searching for.
I suggest phoning them--the order takers are so helpful, and you have an actual person to aid you.
The trees arrived in magnificent shape--I was astounded at the size of them, and the root system. The grapevine was very healthy also, and is actually ahead of my established vines!
Don't let a small difficulty with online ordering stop you from using Stark Bros. It is a good company with good product.