Stun guns and rng

A low ball estimate of the droprate for stun guns farming from normal energy nodes is 20%. That means if you really need one you can farm the 50 salvage in 4 days with free energy + 150 crystals of energy refreshes per day. That's 735 energy per day, so after 4 days you'll have 294 attempts on a 10 energy node giving you 58.8 salvage on average.

So 4 days and 600 crystals. Or immediately and 1270 crystals from shipments if you don't want to divert 4 days worth of energy from other farms. If a team you are currently working on is being severely held up by stun guns you just need to make the admittedly difficult decision to pause your other farms for a few days (or pay of course).

Stun guns in GEC and Shard Shop stores rotate with quite a few other pieces so like the classic logrey example it's not a very low probability event, just a bit of bad luck, if they don't show up for 5 or more days (even when you actually do check at every store refresh). Zetas on the other hand have a very consistent income stream that only varies very slightly depending on TW, GAC and fleet arena results.

You can't do everything even if you spend 1000s and 1000s on the game so prioritise your farms to meet your most pressing goals.