They'll sell a "beef stock" or a "chicken stock" probably, but it's not the same at all.
It's so ridiculously easy to make though.
Just invest $30-$50 in a decent quality slow cooker (one with a removable ceramic pot) and the $2-5 for the bones (I get 'em grass fed), cover the bones with water and let it cook for 24-72 hours. No more effort is necessary really.
I just had a soup I made tonight with stock I defrosted, shiitakes roasted garlic broccoli rabe, and some herring fillets I added just for fun. Damn that was a tasty dinner.
Try it out, it's very minimal hassle with a slow cooker.