This is driving me crazy

Does anyone know if there exists a series of variations on Mozart's theme from the Magic Flute, the one where Papageno plays his glockenspiel and all of Monastos's men go away dancing?

Yes. Google found me Fernando Sor's Op. 9, for guitar. It wouldn't surprise me if there are others, though.

Fernando Sor's Opus 9 Variations on a Theme of Mozart

In total there are 6 variations (including the Coda)

It's quite a good piece of music, I myself have played it on several occasions, so I'd highly recommend it

EDIT: crap, Eldkatt beat me to it :P

If I'm not mistaken, Beethoven wrote some variations of a theme from The Magic Flute for either cello and piano or just piano...

Edit: Yes, it was for piano and cello, but was variations of the Ein M

I just wanted this particular piece because I heard it on the radio once and I haven't been able to find it ever since.

PS: I'm wiritng my own variations on it, but they probably won't be ready for some time.

I too have played the Sor variarions, a fun piece, and not too difficult :D

Are there any for violin and piano?

Well, assuming you're a composer, I suggest that if you can't find any for piano and violin, try composing them yourself. :)

Good luck. ;)