you might want to call Soundtrax they might know of another option. I doubt Bachman will rerun them unless they produce another run of locos with is not likely.
Actually Rick I contacted them at the same time I contacted Bachmann (referenced above).
This was their response:
I would say the TSU-2200 is the better bet, the reason being that the TSU-BH2 is designed to replace the SoundValue decoders specifically and I believe they use a different board format then the On30 mogul that you have, so it is very likely the TSU-BH2 would not fit, you could probably still use it however it would be no less difficult than using the TSU-2200. (maybe even moreso as the TSU-2200 is a bit smaller, and doesn’t need specific provision for mounting)
Let us know if you need any further assistance.