According to the article attached, the oil yields from flowers of the three ornamental Passiflora hybrids (Passion flowers) ranged from 0.022 to 0.038% (%, w/w). Taking in consideration that the density of the Passion flowers essential oil may be near 0.90; you need a total mass of essential oil of 4.5 g (5mL x 0.9) corresponding to the 5mL you need.
So if you are to obtain this 5mL essential oil from flower, you need 20454.5g (4.5/0.00022) to 11842.1g (4.5/0.00038) of fresh flower of Passiflora.
But, this is just an estimation considering the yields data from the attached article. You should Keep in mind that the yield of essential oil of “Passiflora” may varied according to the geographic localization, the maturity stage of the plant, the harvest season and the genetic differences within Passiflora genus