Not specifically minimum gauge, but with O9 and G9 modellers here, I am looking for a small N gauge chassis. no longer than 35mm max. The Kato chassis would be perfect if it as shorter, but there are some other small N gauge locos which cost a lot more. Alternatively is it possible to cut the Kato chassis down? Not something I would want to try but the Kato chassis is cheap enough.
I might have to resort to motorizing a wagon to push loco. Possibly a better solution, and cheaper.