There are quite a few resources you can use to search for information on all aspects of G-scale trains. Their wide popularity has generated dedicated websites, G-scale train clubs, and national and international organizations.NMRA The National Model Railroad Association has a great website as a place to begin. This website is for all scales of model trains, and thus you will need to dig a little to find what you are looking for. NMRA is a non-profit organization that was formed for the encouragement and growth of the model train hobby around the world. With 17 regions across the world, they are one of the largest model train organizations in existence. As with most organizations, NMRA holds periodic conventions where enthusiasts can learn from others, share their own layouts and locomotives. The NMRA website has links for electronics, clubs, hobby shops, tourist sites, and the railroad industry among others. This is a great site to check out if you are interested in model railroading.
Another website where you can find information on G-scale trains is Rail serve. Although the website started in 1996 as a resource for railroad travelers, it has grown over the years to be a resource for all things about railroading, both actual and models. This website now boasts thousands of permalinks covering over 150 categories in countries around the world. Almost every railroading publication has mentioned this organization, and it has won numerous awards over the years. Bookmark this site as you will go back to it over and over as your interest in the model train hobby grows and grows.
If you live in a larger metropolitan area, there is a chance that your local hobby shop may have information about G-scale trains. More likely, you should look for local shows, swap meets, and railroad museums to find information and learn more about these large scale trains. Since these scale models have been around for some time, there is a large amount of history and thus historical information about them. Online forums are a great source of information. If you don't see a thread about G-scale trains, start one yourself. Ask questions, and others with more experience with these beautiful trains will be more than happy to answer them. A recent search of mine in one forum showed over 150 model railroad enthusiasts online in that forum at one time! It's like a virtual meeting of people with similar interests. It probably goes without saying that searching on Google is a great way to find resources for model trains. Here are a couple of tips to help you with that search. First, if you are searching for a specific phrase like "G scale trains" make sure you include the quotation marks. If your results show a large number of sites that you are not interested in, and they include a common word, you can redo the search and omit that word by inserting a dash in front of the unwanted word with no spaces in between
eBay is another great source of parts, but be sure you are dealing with a reputable dealer with lots of positive feedback in their profile.