I read posts that suggest it's a modified IH434 made in the UK.. I'd suggest asking here, they have quite a few parts for that model, you'd have to ask them for help sourcing the parts you need.
Case IH 3434 (Industrial) parts | UK branded tractor spares the same shifter fork and sliding gear were probably used in several models, and possibly by other manufacturers, since it saves huge costs not having to redesign parts for each model, and stock them.. btw, the shifter fork can be repaired by a good welder, checked by a machine shop, and then properly heat treated, the sliding gear can be made by a machine shop with a gear mill, then properly heat treated, it's cheaper to find these parts already made though..