No, there aren’t. Can’t prove a negative, but I did go through all of the prestige classes listed on d20PFSRD.com and didn’t see any (there are a lot, though, so I was going kind of quickly).
Moreover, I can also say with some certainty that this was not a done thing in D&D 3.5e, which Pathfinder is based on, and which had much, much greater emphasis on prestige classes than Pathfinder does. It would be nigh-impossible to speak categorically about the prestige classes in that system (there were literally thousands), but as someone who has been a prolific 3.5e and Pathfinder homebrewer, as well as occasional freelance third-party author, and who wrote a “book” on designing prestige classes, I come from a pretty strong place to characterize the general trend: ability score requirements for prestige classes was not done there, either.
What is done instead is feat requirements, where feats can have ability score requirements. This follows a general trend of prestige classes not having “hard” requirements, but “soft” requirements (e.g. the game rarely says “Xth level” is instead requires a certain amount of BAB or skill ranks you can’t get before that level). In the particular case of ability scores, using a feat instead of a hard requirement in the prestige class opens up the possibility of another class granting that feat as a bonus feat—without meeting the prerequisites, including the ability score requirement. This is consistent with the system as a whole, which allows a wide variety of different ways to accomplish things, and is a feature well beloved by many fans.
Finally, I want to part with an insight I’ve gleaned over the years: prerequisites are... not super great design in the first place. They serve three general roles:
They indicate the sort of person who enters this class, on a fluff level. This is good, up to a point.
They balance out the prestige class, with onerous requirements opening up greater power. This is pretty poor design from a balance perspective, as well as from a gameplay perspective—the more those requirements lock in certain decisions, the more two members of that prestige class are forced to look the same. This is bad.
They allow the author of the class to dictate how the class is to be played. This is awful.
There are myriad better ways to accomplish these goals: the descriptions and mechanics of the class itself should be accomplishing all three on their own. So overall, I favor prestige class designs that are internally balanced, rather than relying on prerequisites to balance them out, and that therefore have light, flexible requirements that open things up to player customization and concepts.
Ability score requirements would fly in the face of that, hard. Ability scores are not easily obtained at all in Pathfinder—whether it be low odds on the rolls, accelerating point buy costs, or punitive prices attached to ability score enhancements, Pathfinder is a game that only supports characters who can focus on at most two to three ability scores. An ability score requirement says anyone who isn’t focusing on the ability you require can’t play—or worse, it doesn’t explicitly say that, and invites players to step into the trap that is trying to pump too many ability scores.
Any given design is going to be different, and I don’t know what you’re ’brewing. Generalizations can easily have exceptions, and I’m not in a place to say yours isn’t one of them. But I can say that I would give that requirement, a long, hard, critical look, and it would be very much up to you to convince me that my generalization doesn’t apply in your case; it would be an uphill battle.
