Finding one is going to be difficult and expensive. I have one on my Beaver but was lucky it had the reverser when I bought it. I don’t use the tractor anymore but had plans of restoring it one day. It’s been sitting for about 7 years because the sector shaft out of the steering box broke. It also needs rings so I was just going to rebuild the engine.
When I bought my beaver I had talked to some people about parts and was told then that they would give me $1,100 for that reverser. They sold parts and was going to resell it. That was in 2001.