I get Ravifruit frozen passion fruit pulp at restaurant wholesalers that are open to the public and in specialty pastry equipment shops. I also recommend Boiron’s fruit pulp if it is easier to find for you.  You can also check out your closest Asian market. They sometimes carry a sweetened version in the frozen section. However, you will need to adjust the sweetness level to your taste and might even need to add some acidity with some additional lemon juice. If all else fails you can make it yourself by cutting open a couple of passion fruits, scooping out the guts, and straining it out.