I have a standard mast configuration. At the masthead there is a "beak" designed for the spin halyard. In my case there there was no block, I had to shimmy up the mast a few times to add a U-bolt and a block. With that done, I could run a dedicated spin halyard.
I should say that over a few years use, I have only flown genny/chute once (odd combination of wind angle and very light winds) - but a dedicated halyard is a good idea anyhow, for a number of reasons, redundancy being a big one.
As for a source...my first I got off Craigslist. My second (I have lightweight, 5-10kn, and heavier, 10-15kn) came from a friend. If I wanted to get another for some reason, I would buy a kit from Sailrite and make it myself!
Good luck....