The one marked as RO-PS-3000Int needs the following pump:
http://www.coralvue.com/reef-octopus-bubble-blaster-3000-skimmer-pump
The second one looks like a CLSC-200 but it is hard to tell without knowing the exact dimensions...
http://www.coralvue.com/classic-200-internal-protein-skimmer
The third one looks like a CLSC-110EXT (body diameter 5") or a CLSC-150EXT (body diameter 6") but it is hard to tell from the picture...
http://www.coralvue.com/classic-110ext-recirculating-protein-skimmer
http://www.coralvue.com/classic-150ext-recirculating-protein-skimmer