Well, just keep an eye on everything that comes out. You'll find more often than you think some good deals. Give it some time and put them back on auction/sale after a good while or whenever you see there's a gap in that kind of merchandise and you'll find you can sell most of the stuff with a good profit.
A friend of mine has done that for a good while with vintage aircraft helmets and has yet to lose any money when reselling (the reserve thing works wonders)
EDIT: Oh and BTW, my friend doesn't do it, but if you are into restoration or if you can adapt those helmets for use in General Aviation, the profits can be much more handsome.
Daniel
