Only venusaurite and scizorite are found in loot balls. Some mega stones aren't in the game, but the ones that are (except venu- and scizorite) are given as official tournament prizes or from spawns from the researcher.
Kihu's idea is gud, raise TP fee by a bit and also make an NPC that gibs u some random mon with the rarity of getting a leggie low, so peeps still buy box and u admins still get ur wages