No, there is no analogue of the blackguard in the Pathfinder ruleset. There is an antipaladin class, but it is written for warriors who have always been evil, rather than for fallen paladins. As an alternate class for the paladin, you actually can’t become an antipaladin if you have paladin levels, even if you are an ex-paladin. You can’t even use the retraining rules, unless you want to retrain everything as some other class and then retrain again to antipaladin. Nor is there any official rule for swapping paladin levels to antipaladin, as there was in 3.5e for high-level ex-paladins becoming blackguards.
Which means that fallen paladins are, in Pathfinder, even more thoroughly shafted than they were in 3.5e. The falling mechanics are, quite simply, awful and atrocious, and while they always were—and the blackguard didn’t help much, more on that in a bit—for Pathfinder to make them even worse is concerning. It’s bad for the game, bad for the story, and just all-around bad. What should be the height of drama is instead this huge anti-climax where a fallen paladin just gets crippled and all but forced to retire, rather than become any kind of significant force for evil.
In 3.5e, you at least had the option of the blackguard class... sort of. Unfortunately, the requirements for blackguard—including numerous skills that paladins don’t get in class, and feats that are unlikely choices for a paladin (or anyone, really; Cleave and Improved Sunder are seriously poor feats), blackguard is basically not an option for an ex-paladin unless they were planning to fall all along. Both 3.5e and Pathfinder have very severe problems supporting unplanned character development in general, but the blackguard is a particularly extreme case where it really only makes sense if it was planned, as a metagame thing.
Later editions of D&D do a better job here, where 4e eliminates falling altogether, and 5e provides rules for an automatic and mandatory switch to some other class (so even though you’re forced to lose your paladin features, you at least get the features of some other class, rather than being reduced to NPC-class status). D&D 5e also had the oathbreaker paladin archetype, which is an analogue of the blackguard for that system. But Pathfinder doesn’t have that.
Ultimately, because the falling mechanic is so bad, I mostly recommend ignoring it entirely. In my games, a paladin falls only when her player chooses to have her fall—at which point the paladin levels are immediately swapped to another class (à la 5e), or paladin features are swapped to alignment-flipped versions (poached from blackguard and/or paladin of tyranny or slaughter), or the character is retired. At no point is the character crippled and reduced to NPC status, and at no point is the player forced to play a character they don’t want to play. This ends up being the same in both 3.5e and Pathfinder for me, since the blackguard itself offers a poor solution to the problem the falling rules create.