The part number for that gearbox is 248279 which is discontinued by NH. They may be able to cross reference the number and tell you what other models it was used on. They still have most of the parts to rebuild it but not the housings.
I don't think newer combines had that gear box, only the TR70 did. Not sure about the 1400 and 1500's, been a long time sence I looked at one of those. If you need the whole gearbox I would try a salvage yard. If you can rebuild then I would do that. Seems to me that maybe a bubble up auger gearbox from some TR's can workIJ I think sombody told me that once but I am really not sureIJ
The bubbleup gear box is the same as the unload unless its an update on the bubbleup. We have an 86 with that style on the bubbleup so its used on several models. When you replace pay close attention to the stop collars for centering. Misalignment will eat the shaft and_or couplings up fast. Also if you rebuild I think it helps to have a little tighter gear lash then they are predesigned for. You can grind a little off the ends of the shafts where they contact the center pin but its guess work as to how much and they should be ground the same. In my opinion they are not the best designed box for the application. fwiw