I am pretty sure the OP is on to something because we keep getting these gun smith bounties/quests from a found weapon fragment that weapon depicted in the mission emblem looks like pocket infinity. I believe the first step is to finish 10/20 or more of these bounties/quests and level up the gun smith to Rank 5 and a quest will pop where you need Pocket Infinity to beat a mission that makes the Black Spindel mission look like a joke.