If you assigned the Lucky Bastards Rogue Crew to a fleet and did not find any blueprint pieces, you may have not been hitting salvages at the correct level Blueprint pieces are organized by tier; not all blueprints are available at each tier (click here for a list of which blueprints belong to each tier). This means that there are some blueprints that are only available from low-level salvages, some that are only available from mid-level, and some only from high-level. If you already have all available blueprints from one tier, the Lucky Bastards will not guarantee a blueprint drop, as there are no blueprints at that level left to find. Try hitting a variety of different salvage levels if you're not finding what you're looking for!
The Lucky Bastards only work on salvage fleets and Draconian Mining Platforms.