Pepboys has the Cornell 1000's in a whitewall in 225/75/15. I know this because I just had a set of 4 I sold. That tire is what came stock on the WAGONs and is extremely close in height to what came stock on the 94-96 SEDAN. I've used anything from a 215/75/15, to a 235/75/15 on Buick sedans, wagons, Caprice, etc. So long as they are close, everything is fine.
225/70/15 is a second option if you can't find them, as is 235/75/15 is you GOTTA have a white wall.
Like 200-OZ said, find a new tire dealer. Yours blows. I have 10 tire shops of different names withing 5-10 miles. And I have Tire Rack's warehouse within 30 miles. If one shop gives me shit, I go on to the next one.
Personally, I find myself hating discount tire more and more every time I deal with them. It's getting so bad, that one of the reps will not even make eye contact with my dad or I if we walk in. They used to be great... Now they feed us a line of BS. It took me 30 minutes to get a tire warrantied out and they refused to let me go without paying for a mount and balance. Then tried to say I would have to pay more because of how old the tire was. Not basing the warranty on it's almost full tread. As soon as I mentioned the numerous complaints of blown outs on this tire they shoved me out the door and cheaply as possible. RIP "Discount" Tire.