I threw together a 7.62x39 pistol recently, one of those “use up spare parts I have lying around” type  builds.
The barrel I used was supposed to be 10.5”, but it’s really like 10.0. So for the time being she’s wearing regular carbine handguards on a GI barrel nut.
I want to add a rail of some sort, mlok (or even keymod IDGAF)

Alot of the 9.5” type rails cover too much of the threads: I will be adding a suppressor with qd mount, so I need access to the threads.

Everywhere I look I see 9” rails, that upon closer inspection are really 9.4” or 9.25”

Who makes a 9” rail that is an honest-to-god 9.0” long?

SLR Rifleworks

3/4" difference is normally where I shoot for. So 9.25 should come right to the shoulder of the threads of a 10" barrel. Did you measure the barrel with a rod down the barrel against the closed bolt face?

This is an 9" Aero Atlas R-one on a 10.3" barrel. The rail is actually 9.125", but there is still space before the shoulder.
Attached File

Daniel Defense Omega 9.0 M-Lok spec is 8.99".  I'd call that verrrrrry close.

https://danieldefense.com/omega-rail-9-0-m-lok.html

Saw the DD omegas were right there, but couldn’t find any in stock, so I decided to go with a Vltor Freedom keymod 9”

It worked out to like 8.875 inches. Just the right amount of clearance for a SiCo ASR mount (Pics incoming, cause why not)

For those that didn't understand why OP was asking, read this

DD makes 9.0" rails compatible with a 10" barrel.