speedo problems

[neo71665]

I'm posting this here instead of drive line cause its related more to 4x4s than 2x. In my 87 blazer I lost the speedo and so far have replaced the driven gear and cable. I have found out GM is gonna stop making the silver 20 tooth reverse rotation driven gear I need but I found one. The question I have is does anybody know what the factory drive gear is? I need to try to order one (if they are even still being made) and the tooth count and color would be helpful. It has the NP207 transcase with 235/75/15 (don't think those are factory size) and 3.73 gears. I tried to do the calculator but have no idea what the speed revolutions are on a dimes speedo.