Cammy never carried a gun in the movie itself.
However depending on a variety of factors, i.e.
the size of the "cel", line and paint quality, and
price you saw it for, it might've been a) a tester
cel, b) a hanken (though I doubt it I've seen
years of SF2 merchandise and I've never seen that
image of Cammy), or c) a fan made cel.

Whatever it is, I would NOT rush to buy it if I
were you. Do more research and ask the seller or
owner where they got it, ask for proof other than
their word (really meaningless most of the time),
and ask for proof if they claim it was a hanken
used for a product or ad. Otherwise screw it, if
you like the image get a fan repro done for cheap.