Are you sure they're not dropping? They didn't before yesterday because there were only primary ammo sidearms in the game, so there was no point. According to light.gg, all of those mods have been updated in the past few days, and the finder and scavenger mods now specify special ammo. This would suggest they may be dropping again. At worst, you may have to wait for Banshee or Ada to have them on offer.