I have found bulk packs of chicken (plus chicken liver in one pound tubs) at a market that caters to the Hispanic population, plus bulk packs of chicken wings at Costco ($11 for 10 pounds), but I have not found sources for anything more interesting. The butchers in town can order stuff, but the quantities can be a problem (50 lbs. of venison at a time?) so I have not gone that route.
I will be interested to see what others have suggested. Laurie, that link is interesting...
I just use grocery stores because I can't drive and my parents don't want to take me to Asian or other ethnic grocery stores that may have more organs and interesting meats that our culture doesn't use too much of. Liver I can get no problem at the store. Chicken, pork, beef and turkey can be bought at the store. Kidney was a pain in the butt but my grandpa called around and found a store that had it a few towns over. BUT if you want to make the best of the diet as far as price goes then getting stuff over the internet and from local butchers works best. Butchers will give you things that people have no use for like chicken necks for cheap/free and over the internet you can ask for (don't look, ask) meat with freezer burn that people want to get rid of and get it for free.
I get most of my raw meat from China town. I feed both of my cats and a German Shepherd Dog raw, so I have to pick up about at least 10 lbs of raw food weekly. China town is great since they often have "old" whole chicken for about $1.50 each. The best thing about China town is they tend to have a variety of organ meats such as hearts, livers, kidneys, and untreated stomachs for a great price.
I also go to Costco and buy those packages of chicken wings, specifically for the cats. Also, in the frozen foods section, I pick up packages of frozen whole sardines for all the animals. I am currently looking for a good turkey supplier to broaden their diets since the cats for whatever reason, cannot keep beef down.