I put aboput 100 Vallejo and Reaper paints into used 
GW and P3 pots (yes, heresy!) 

  I also use 
GW empties for a bunch of liquitex products, like Gesso, ultramatte/matte medium, pumice stuff, modelling putty, etc. 
 I also have 
GW Lahmian Medium in both the original 
GW pot, and in an eye dropper, and about 50 
GW paints mixed with airbrush thinner in eyedroppers 
 
  Sorry I'm not much help about buying more P3 style pots though.  Use more P3 paint?  They make good paint! 
 I seriously wish these companies would make all their products in both droppers and pots.  Although I prefer pots most of the time, situationally, there are times when both are advantageous.