barrel lengths

Wondering if there exist barrels for airforce rifle other than 12″, 18″ & 24″. I’m looking for .25 caliber around 15″ or so. The reason is that I got a new screw-on moderator (1/2″ UNF, very very effective) and would like to use that on my TalonP. Right now, I have an end cap adapter that I use for the moderator, but I would rather get a threaded barrel instead. The 12″ barrel that comes with the TalonP is recessed inside the frame, I need about 2-3″ more. I could get the 18″ barrel but would prefer to keep it as short as possible, that’s why I bought the TalonP in the first place.

The extra length would give me a few more fpe and quiet the rifle a little too. So in summary, where can I get a barrel about 14-15″ ??