Scumbags!
Sorry to hear that, what a shame that a couple of shi*$ can ruin it for all of your other customers.
Is a mini-veggie box scheme practical for you? If you had say, four/five different types of veg in one of those old greengrocers boxes? People at work have offered me £5 a week for this in the summer (including 6 eggs).
Could you leaflet or advertise in local shop windows?
Also, I second the local resteraunt idea - a friend of mine has a resteraunt and regularly buys ad-hoc things from local people - truffles, golden wonder potatoes (apparently not easy to get hold of) and just ordinary homegrown veg. He then uses them for a 'special' - so doesn't require regular supply or large quantities, and charges a premium because they are 'local homegrown'.
Good luck with whatever you do.