In a Passiflora biological taxonomy document I read a few years ago, they grouped it into the Passiflora "Super-Section Laurifolia / Series Tiliifolia", which would maybe suggest that those in the same Super-Section and/or Series would make for the best cross pollinators. Looking through the list of Passiflora species in that Super-Section, these are the ones that are more commonly known:
P. gabrielliana
P. laurifolia
P. nigradenia
P. nitida
P. tolimana
P. venusta
P. alata
P. phoenicea
P. quadrangularis
P. maliformis
P. serrulata
P. triloba