Keep trying to get them! They seem to be a decently common drop, and it is possible to get a double drop as well.
Personally I use Ngens for physical BP and Punga/Nares for attacking/idle, depending on the situation.
Generally only pull out af3+2 legs for Magical BP or siphon
Just to piggyback on to this, if you
only use 5/5 merited magical BP's, it's my understanding Ngen wins out over Caller's Spats +2 for the Rage pact itself when TP is at 275%ish. You won't have 275% TP in every situation but it bears noting. I do the same thing you do though: Ngens for physical BP and Caller's for Magical BP.