Years ago, I had John Kopec do one for me (though I suspect Eddie Janis actually did the work).
Works perfectly in all of my Colts.
Colt's Custom Shop 'will' supply a .45ACP cylinder, and has - but they want to fit it and I have no idea how long that might take.
This isn't Rocket Science, by a long shot - I'd imagine there are a number of guys who can do the work, so start loking for an appropriate cylinder - a .357 Magnum or a .44.
Good Luck - if you get the work done, you'll really enjoy shooting it.
Vaya,
Scouts Out!