Roundhouse also makes a two truck and three truck shay in HOn3.
Roundhouse also makes an unpowered 0-8-0t engine using the 2-8-0 chassis and a saddle tanker body. You could easily power it by adding the gears and motor from the latter or get a NWSL gearing kit. Here's a picture of mine:
I believe Grandt line makes an HOn3 boxcab diesel that is affordable (or at least they did)