welcome to the forum - I made it so you'd get notified
A barrel is easy to find, they are on ebay for $50-$200 - depending on condition, length, etc.
9mm is the cheapest to shoot, of course you can find 7.65mm (30 luger) barrels because of that easier.
Any barrel I have had GT or Lugerdoc put it on for me, it can be slightly tricky I have been told.
Ed