I dont know, during this time of year..
Where are you located? Most grapes are locally sourced, or through distributors where the grapes arrive shortly after harvest time, having been pre-ordered and paid for ahead of time
They dont usually 'keep' very well, unless frozen as juice pails
Looks like a forum sponsor, Wine Grapes Direct, has some California grapes for sale, but the WA/OR area isn't quite set up with distributors like Cali & the Finger Lakes regions are.. Why, I'm not sure..