I think that instead of just flatout buying the weapon, Bungie makes "paid bounties" meaning that every weapon has a custom bounty that can be purchased. For instance Gjallarhorn was "forged from the armor of those who died at twilight Gap" So: Step 1: buy rocket frame from crucible vendor Step 2 purchase exotic rocket synth from Xûr Step 3: honor the lost: win 5 games on twilight Gap ( in a specific "twilight gap" playlist avaliable only to those who have the bounty) Step 4: give Xûr a piece of legendary or better armor for each class to acquire memorial armor Step 5: Give gunsmith memorial armor and rocket frame. Step 6: bring acquire strange medallion from Xur Step 7: give gunsmith strange medallion in exchange for Gjallarhorn. This way people still "earn" the weapon.