John,I think 1/32, 1/29, 10mm to the foot, are normally refered to as gauge 1. Whereas the OP is specifically asking about G scale - ie 1/19, 1/20.3, 1/22.5, 1/24 - so the short answer to his question is - there ain't no such thing - at least not to my limited knowledge
We try to avoid specifying that "G scale" is anything, as most modern outline standard gauge guys who run 1/29th think that they are also using "G scale". It's just too open-ended a concept.
I suspect the Original Poster ("OP") was looking for something that runs on his "G gauge" track, i.e. 45mm gauge and possibly code 332. I doubt he was focused on the scale - and the fact that he asked for "G scale" merely demonstrates he probably wasn't.
I agree with Greg that the simplest and least expensive option is perhaps the USA Trains model in 1/29th.