NV3550 to AX15 Transmission Swap

There used to be a company that could retrofit the ax15 with a 4.3:1 first gear out of a similar aisin transmission that was sold in japanese markets. My research of this came to the parts being extremely difficult to come by anymore.
I think those were from an early model toyota pickup and one of their weird Japanese cars that had a V-12 or a big V8 in it.