Lothar Walther has a factory in Cummings, Georgia - http://www.lothar-walther.com/barrel-blank/airgun/?p=1 - and they have a huge selection of airgun barrels available. They will also order a specialty barrel for you from their factory in Germany - http://www.lothar-walther.de/163.php - if it pleases you. Just remember that Walther only sells barrel blanks so you will have to find a machinist to cut it to match the profile of your existing barrel so it will fit on the gun. Some barrels are crowned and some are not, so your machinist may have to crown the barrel for you also. You may purchase the barrel with standard or polygonal rifling, and you may decide on choked or unchoked. Many barrels are available in stainless steel...and all steel barrels are shipped "in the white" which will necessitate having the barrel blued or cerrocoated to protect it from corrosion.
Always the best, Chuck