Check out
www.bricklink.com www.ebay.ca www.pldstore.com
Bricklink sells everything Legos, don't buy stuff from Germany, shipping rates will kill you, and ebay.... pretty self explanitory, and for pldstore.com, you can buy basically any part there, but it's all in bulk. I'm not sure if you can get RIS there, but you can get the RCX for 120$
ripoff! Check out bricklink for sure though.