Potential patrons are supernatural beings the PCs know about. So, in an ongoing campaign, some options may already be known, whereas others are introduced during play.
Appendix N is chock-full of beings that could be considered patrons in DCC. Elbereth in Lord of the Rings never makes an appearance, but in A. Merritt's work, patrons make direct appeals to the protagonists, and are actual beings in the world. In Moorcock's work, Elric already knows the potential patrons of his people, and the various entities folks call on in HP Lovecraft might be located by research into the Necronomicon or other benighted tomes.
I have written several adventures that put PCs into contact with potential patrons - the Black Goat, the Cinder Claws, Doctor Chapman, and Somnos, for example. I am not alone in that; Malloc gains a write-up in the Sunken City Omnibus, and there is a potential patron in The Mall Maul for Crawling Under a Broken Moon (issue #2, I believe) that one might join with when encountered. Silent Nightfall introduces demi-patrons, suggesting (as with the fruitcake in Perils of the Cinder Claws) that there are ways to enter symbiotic (hopefully) relationships without using a full Patron Bond spell.
Other patrons are entities that the PCs may themselves seek an alliance with because they are part of the known backdrop of the game milieu. This includes whatever patrons the judge says it includes....beings that everyone in mystic circles know to be seeking to win friends and influence nations.
In general, I would say you should consider a list of known patrons, patrons that are effectively potential rewards (or punishments) for playing specific adventures (or making specific choices), and dropping the occasional patron reference into arcane works found in adventures...effectively seeding them like treasure maps, which the PCs may then pursue or not. For example: A plague spirit may be encountered in a certain graveyard at a certain time of year. Take it or leave it.
And, really, consider the demi-patron model: I am not bound to you, but I can call on you for (say) spellburn...although there is certain to be some cost...perhaps some form of patron taint.
See also: http://ravencrowking.blogspot.ca/2012/0 ... ssics.html