The proton ones aren't super rare but there aren't very many I think theres like 10 guaranteed the rest are random spawns the inverse proton ones are super rare I think theres 5 guaranteed and they have a much smaller spawn chance kinda a bummer too if your into melee they do really good damage for thrown weapons.
I think you'll probably find the
proton throwing axes on random spawns, but the proton
inversal throwing axes are very limited. Or are the regular ones limited too?
Seems a hell of a waste having single use weapons in very limited quantities. I don't use them simply for the fact I see to miss half the time with thrown weapons, so I'd rather horde them for display somewhere.