In my experience calling always gets you "We do not sell to the public" answer.
Being there in person on the other hand sometimes will make a difference. Look for a smaller scrap yards.
The same with tire shops - stop at every one you see, avoid the big chain stores - small, used-tire places are your best bet. Expect to pay from $5 to $75 per 5 gal bucket. My best deals have been at custom wheel places - those shiny 22" rims take a lot of stick-on weights, that cannot be reused. One time I got close to 400lbs from one store.