In Lead We Trust makes threaded barrels for both 32acp and 380 variants of the 1903/1908
No need to wait for the factory ones!
I have one for my 1920-ish 1903 in 32; took a little fitting to get it to fit. When I told the guys about my issues they asked for the barrel back to see what they would need to alter in future runs and refinished it for me. Apparently they had been basing theirs on the new made guns (at the time) and didn't have a whole lot of earlier guns to compare them to...at least that's my suspicion.
Anyway. Now to find mags...InterArms in TX used to have a pile of them, sadly I missed that boat for 380 mags...
Edit - I don't remember the serial number cutoff, or dates tbh...but at some point in the early 1920s Colt redid the hammer to add a safety/half cock notch. I want to say the serial cutoff for the 32acp was in the 300k-s? I could be wildly wrong; a quick google isn't giving me the info I'm looking for but I'm sure it's out there. Anyway...not that it made it
that much safer to carry, but it's the primary reason I don't carry my 1903 - the serial pre-dates the half cock notch and I've read too many stories of people getting killed by their own gun (albeit because they weren't using a holster and it fell out of their waistband, or it fell out of their ill-fitting holster, etc)
Or like the story above...if the gun never left the holster and it went off because he fell on it, oof