I see it frequently in America.  It’s a homonym of the contraction *would’ve*, and similarly, other modal verbs like *could’ve*, *should’ve*, *must’ve* and *might’ve*.  (Not, however, for “can have,” and very rarely for “will have.”  I personally don’t contract “can have” in speech, but do contract “will have*.)  With negative contractions, *won’tve* and *wouldn’tve* are so rare that my spell checker doesn’t recognize it, but I pronounce the word *have* in *won’t have* the same way as in *will have*, when they’re both stressed or both unstressed.

Another variant is “Woulda, coulda, shoulda,” or “Wooda cooda shooda,” which writes out phonetically an even more-reduced form of unstressed *have*. This is more informal than “Would’ve, could’ve, should’ve.”

Since there are many verb phrases that do use *of* (for example, “Be of service”), it’s an easy mistake for native speakers to make.  It’s likely to become an accepted synonym of *would have* eventually, but is still considered an error by people of my generation.