Where can you buy 7.65x22mm Longue ammo?

Can't promise anything, but I'd recommend you try Classic Arms in Indian Trail, North Carolina @ 704-684-0650. Bear in mind that there is more than one company operating under the name Classic Arms - you want the one in North Carolina, not the one in Michigan. If they don't have it, they might be able to point you to a place which does have it. You can also see their website by following the 'Related Links' section below.