Edson, by far the best resourse for garage kits is a magazine called Amazing Figure Modeler. Actually, I just got my latest copy in the mail yesterday! So that information will be some of the most up to date you can get right now. Check out thier web site as well, many great links to explore (
http://www.amazingmodeler.com/ you MUST go to the links page, you'll spend an hour there just exploring!)!
Carl's sugestion of the Clubhouse forum is spot-on! It is the best web site for asking questions, and for knowledgable folks on all things "garage"!
There is also a retail web site that has been around for a long time that caters exclusively to garage kits, and can be a source for older kits sometimes, it's called X-O-Facto (
http://www.xofacto.com/).
If you're after older kits, I almost hate to say it, but eBay can be a good source. MANY of these kits are manufactured in very short runs and can be hard to find if you didn't get in at the begining of a release. If you do decide to go that route, all I can say is be careful. Be sure not to buy any re-cast kits if possible. Be sure to make sure they are a reputible dealer and if they are selling kits out of the far reaches of Hong Kong, or a far east country at rediculously low prices, and without "manufactures box, box art or instructions" you can bet they are selling a re-cast kit! Good luck!
Jay H.