I played like 400hours this wipe and i can tell you i did find more than 100 flashdrives.
Loot All Safes as much as you can (Factory office since spawns are even more aids than ever before you can rush office most of the time )
Looting woods tent close to sawmill at the coast will also bring you one every second or third raid.
Filling Cabinets have also a chance but smaller than woods or safes.
Don’t look at Pcs. The spawnrate is almost 0. Never found one sticking on a pc like back in the days.
Jackets also suck.
Customs Safes, Shoreline Pier Safes, Factory office or Shoreline Cottages. Just rush that with double barrel or pistol. Make it outa after killing 1 scav.
Should take you max 3 raids to get one on customs. Go Nighttime and go only 3 story doorms if u have best spawn. Otherwise start with 2 and only loot big red or gas station. will still work 😉