Paul hit it right on the nose. The size of an entire side can be overwhelming in comparison to what you got, a single shoulder averages 6-8 square feet, a side can average 20 and larger (I found one once that was 30, what a beast)
I had heard at one time that W&C was working on doing some double shoulders? Not sure how that went.
When browsing Tandy, or The Leather Factory, its wise to dig, all the way to the bottom if needed. Look at the back and front carefully. As Paul said, you will come up with some with a "stringy" back, not good stuff. Thats whats referred to as a "soft hand" loose fibers can cause so many issues.
Look for an even, fuzzy feel to the back. The edges will probably still be stringy, but you can work those into welts and such. Watch for soft spots, hard to see but easy to feel out.
Its possible to get a nice chunk of leather from Tandy, you just have to dig for it. I'm lucky to have both a Tandy and TLF within driving distance so if one doesn't have what I need I'll simply go to the other.