I'm out of G for about 5 years now so this may not be up to date.
Unlike the other scales there is no standardization in G. Bachmann and LGB are either 1:20 or 1:22 or maybe one of each. Aristocraft (out of business) and USA Trains are 1:29 and Williams Trains are 1:32. Most couplers and track do not mate with different brands. Try a search for Large Scale Online or My Large Scale for a forum.