good glucosamine/chondroitin source?

i've been hearing that glucosamine/chondroitin are really good for joints and helping relieve arthritis pain in people for years, now i've heard that it's good to also give to our pets
i was just wondering if anyone here has found a good source for buying this stuff either online or in a store.. or whatever
i've heard some people say that they've found places that sell it fairly reasonably priced by the bucket.. for horses
and they just measure out the proper amount for their dog, cat, hamster, gerbil.. whatever.. etc..
this is what i'm really interested in but i'll really take just about anything i can find :)

thanks
Kim