I'm going to say "No", there isn't, and I'm going to say it confidently, even though my case isn't airtight. Rationale (you'll understand me not posting clips, I trust :)):
Vibrators, in general, have appeared in movies about as long as movies have existed. But they couldn't have appeared in any mainstream (US) film prior to 1968, when the Hays Office was replaced with the MPAA, the year the wand was invented. I suppose, technically, non-wand vibrators could've appeared in the pre-Hays era, prior to 1930 or so, but the things Hays and his supporters were objecting to were relatively mild cases of nudity (and bad behavior). It's inconceivable that presentation of sex toys was ever mainstream enough to be part of the fuss.
Post-1968, mainstream films didn't plunge into the graphic representation of sex right away, though much was implied. The end of the Code meant a lot of grinding, some bare butts and boobs, and a whole lot of talk, to the point where many raunchy films were re-submitted for milder ratings in the video era ('80s/'90s). For example, Turner Classic Movies showed Russ Meyer's once X-rated Beyond The Valley of the Dolls a few years back, I think, unedited.
Even by '84 vibrators are still considered outré enough to be played for laughs in Bachelor Party. These are professionals, women so addicted to sex they do it for a living (or something). "Bachelor Party" (and the more successful "Police Academy") were the "Hangover"s of their day. Meant to be outrageous, edgy comedy.
"Sex in the City" was thought of as provocative in its discussions of sex and masturbation, even at the turn of this century.
So, no, the Hitachi Magic Wand never appeared prior to this film. Bachelor Party may even qualify the first, em, graphic vibrator in a mainstream (US) film. You can find sweat-box-like devices that give orgasms in films like Barbarella and Sleeper, and actual phallic vibrators in less mainstream films (Russ Meyer), but not vibrators in mainstream films, much less this brand specifically.
In fact, I'd go so far as to say the presence of a vibrator rules out the possibility of it being mainstream. The late '60s/'70s/early '80s just weren't down with that. Phallic sex-aids do make the occasional appearance, in a few at least marginally mainstream movies, as listed below:
Kentucky Fried Movie has a dildo in it, played strictly for laughs. This is probably the most mainstream of the movies in this list, even though it was more of a surprise "sleeper" hit.
In The Realm of the Senses does, too, not for laughs, but it's also pretty much straight-up porn. Since it's French/Japanese, it gets a lot of critical praise.
The First Nudie Musical has a...uh...song-and-dance number with guys dressed up like dildos. You can find this clip if you Google for it.
And, lastly, a potential technicality: Hardcore features George C. Scott trolling adult stores. It's likely vibrators are visible on the shelves in the background at some point (though I don't recall, and it's been a few years) and that brand may be among them. Hardcore was on the edge of mainstream and not a huge success, but with Paul Schrader directing and Scott starring, I'd say it could count.
It's not perfect but you can validate my claim by looking through BoxOfficeMojo, which has yearly breakdowns of all the movies released going back to 1980. (I've seen almost all of the 1980-1984 range, and feel very strongly about the lack of virbators.)
Clearing the 1968-1979 period is harder. IMDB lists almost 1,500 movies with an R-rating in that time-period (and it would've been R or X rated):
If you look at the most popular, you'll see the first likely candidates for vibrators are things like "Flesh Gordon" or Russ Meyer movies. Oral sex abounds, but not machine-aided. That doesn't rule out a "cameo" like the one in Bachelor Party, but mainstream sex comedies usually didn't roll that way.
You could also search X-rated films but almost all of those were not mainstream, and the ones that were almost universally were re-cut for Rs (and the exceptions, like Midnight Cowboy are very well known):
Another route is the top 20 films of each year of the '70s:
Again, I've seen these. And I'd remember. =P