Wal-Mart carries 16-oz packages of ground 90/10 Bison (American Buffalo) for about $4.50 in my area. I have been told by my meat guy there that they plan to start carrying other cuts like steaks, roasts, etc. too. As others have said - if you don't see it, ask the guys in the meat department.
As for the Buffalo Burger recipe .... I would never do that to good ground bison! I think bison has a sweeter, less gamy, more delicate flavor than beef and by adding all of that "stuff" (ground chuck, tomato paste, liquid smoke, etc.) you'll never taste the bison! Just make your patties out of straight bison (8-oz is a nice size), grill, and serve on a fresh lightly toasted bun with lettuce, tomato and a thin slice of onion. My favorite place in Denver didn't use anything else - they just pulled the meat off the grill and put it on the bun and put the top on for about a minute (to allow the meat juices to moisten the bun) - then added the lettuce, tomato and onion. No steak sauces, mayo, mustard, or slices of pickles - these were served on the side and few people (except for tourists) ever used them.
My son just brought me a pound of ground bison and that's the way I'm going to cook it. I find that the KISS principle really works some times.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain