Of course you have halyards, one for the mainsail and one for the headsail before the rollerfurler was installed.
I believe you mentioned a Snapfurler, is that the Schaefer Snapfurler CF500 or CF700, I have the CF700. The CF700 uses the jib halyard to initially hoist the headsail up the foil then I furl it from there.
There are other brands such as CDI which make use of an internal halyard thereby making the original jib halyard redundant which then frees it up for spinnaker use.
Someone also mentioned that some foils have two slots so that you can raise the next sail before dropping the first sail but that would entail two jib halyards, something you may wish to consider if your snapfurler is the same as mine. I am thinking of switching my single jib halyard pulley block with a double pulley block to facilitate the use of two jib halyards so that I can have a spare one for a spinnaker. I do not have a spinnaker yet but it is on my wish list and with any luck it will be on my boat next spring. I keep an eye on threads like this just for that reason, I too am on the lookout for ideas.
Spinnaker halyards are simple to add external by adding a bail to the top of the mast if necessary to hang a turning block from. You may already have one. A cam cleat or turning block to run the haylard back to the cockpit. For a asymmetrical, a topping lift and down haul for the pole is not necessary. If you surf the used sails you should be able to find a used one. For a symmetrical chute, you will need to add an additional turning block about the spreader to raise the pole and a turning block mid fore-deck to secure down the pole. this triangulates the pole by the 3 controls, oh the third is the sheet to the clue of the chute at the pole end called the guy. Once you play with the chute in light air, it will become your favorite sail.
On my 525 I have 2 headsail halyards and 2 chute halyards, On my Cal 9.2 I have 2 headsail halyards and just one for the chute. On smaller boats you can use through deck turning blocks to make an internal mast halyard. See the attached pic of the dual chute halyards on the 525.....