in the uk the biggest problem you've got is getting the CNC lathe program for the body of the gun to enable the machine shop to do it accurately. Then going to a machining shop and getting them to do a one off job is expense! you could take it to any machine shop but you risking it with some guy with a manual lathe guessin . . . .
The best bet would be to get it done in the states but obviously you've got all the cost and hassle of shipping.