It's going to depend on what sort of cause of action you allege as a result of the supposedly selective prosecution. Is your claim, for example, based upon a claim of racial discrimination -- e.g., although many people are investigated for similar conduct, the decision to charge shows a clear pattern of racial discrimination? Is your claim that you were selectively targeted prosecuted for your prior exercise of your First Amendment rights? You need to identify the actual cause of action before you can identify its associated limitations period.
If you prevailed after a Rule 29 motion, then the case got all the way through at least the close of the prosecution's proofs at trial before you obtained a dismissal.
For a wrongful-arrest claim to succeed under 42 USC Sec. 1983, it is not only necessary that the officers lacked probable cause to make an arrest, but also that there was no basis for the officers to reasonably but mistakenly conclude that probable cause was present". It's all-but-impossible to show a lack of probable cause for arrest when a prosecutor independently finds probable cause based upon the police investigation, and where the case gets all the way to trial without your succeeding in convincing the court that there is no basis to proceed.

