I just had to replace the crank timing gear on my 20. Bought one for an RB26. It's identical as far as I can tell. Fits perfect. Timing mark in exactly the right spot. I believe that while the Nissan part numbers are different, all the RB's use the same timing gears. I know the timing belts and cam gears swap between the 20, 25, and 26 so makes sense that the crank timing gear would be the same.
Anyway, I would call an engine importer. Check our sponsors. Ask them if they have any bad long blocks that they are parting out.
Could also try this link.
http://www.japanparts.com/db/p...olkey
They only show one for a 26. But like I said, they are identical as far as I can tell. Hope this helps.