I've got a Marlin 917vl that I want to get threaded for a suppressor.  I dont know if the barrel is threaded to the reciever but think its pressed in.

My questions are
Can a gunsmith thread it without removing the reciever?
Who should I send it too if not?

It would probably be cheaper to just trade it in on a threaded savage but it's just such an accurate rifle.  I've got more in the upgraded trigger and spare mags than what the rifle cost.

It can be however there is a chance the bore is not centered though unlikely. I threaded a .17 and the bore was very off center so it did not work out. Being in the receiver is not an issue if the barrel is long enough to fit through the headstock and use a spider. If you don't find anyone local I can assist with it.

There's no need to remove the barrel from the action.

You may encounter some problems. The first being the outside diameter of the barrel. You'll need .500 + a .04 shoulder. Total outside diameter would need to be .580
It could be a little smaller, say around .560
The next problem would be the length of the through bore of the lathe. A lot of older lathes would have a through bore that's too long

I made sure when buying my lathe that it would accommodate a 16" barreled action

The barrel is press fit, but not a huge deal.
If it can't fit through a spindle, a long enough bed won't care (ctr to ctr distance)
Off-center bore can be accounted for (lathe and indicating)
Smaller than preferred muzzle dia also can be accounted for (thread 3/8-24 or 28 and make adapter to 1/2-28)

I believe that it's a 22in heavy barrel from my internet search.

Found a smith close to home to do the threading. Former Gap smith. $125