There are two US-based fora. The first is called mylargescale.com. Some of us from here post there - some of us don't. Greg does, but having had multiple less than useful dealings there, I left a few years back. There are some great people there, nevertheless, like Kevin Strong, Jason Kovaks, Art Gibbs and others. The Bednariks, Charles and Ryan, are a father and son team who operate TRS, a refurbishing/rebuilding/tuning and fettling company that specialises in making Gauge 1 trains go the way they should, even to the point of converting them to coal-firing, or, more exhaustively, from electric to alcohol/gas/coal-firing, in return only for money.
The other US-base forum is called Largescalecentral.com, and many of us here are also on there. Although most posters are US-based, there is a strong following from Canada, Australia/NZ and Paraguay and a few from UK, too. We have a 3D printing maven based in Ottawa who not only makes his own range of large scale products, but can also be prevailed upon to do one-offs. His skills are prodigious, and his prices are extremely reasonable, as I know from personal experience. I'll let Fred Mills give you his details, as they are good neighbours. Right now, a pair of one-off 3D printed truck sides would seem to be the way to proceed without necessarily breaking the bank.
As for getting your truck from UK, I'm afraid that there is no manufacturer of mass-produced 1/32nd scale US-outline locomotives in UK - everything US/Canadian or non-British we have here is imported. There are a couple of very highly-regarded scratch-builders in Gauge 1 that I could put you in touch with, but since you seem to be looking for something of a more 'economical nature' I think I'll hold back on that.
tac
Ottawa Valley GRS
Port Orford Coast RR - Eastern sub.