try ebay or Fatbobs..and yes a PM has cocker threads ..
No it will fire exactly the same distance as any other barrel , if someone tells you that a longer barrel helps you fire further ,laugh in there face ,distance is down to the velocity of your marker
however the APEX or the Flatline will help you fire further due to the spin they put on the ball , however I had an Apex and thought it was **** but thats just me eh