If you contact your local police / sheriff dept., it is likely they will accept them to be destroyed. That's how LE has handled it in most of the places I have lived. In the alternative, next time you visit a public range, you can usually turn them in there and they will dispose of them along with other stray ammo that is either left behind or has ended up on the ground in front of the firing line.
Call first before you trudge down to your local station to surrender ammunition. The department I work for, and many others in Arizona, will not accept or want ammunition from an unknown source.
It is considered a flammable-hazardous substance and it requires specialized EPA approved methods of disposal when destroyed. The lead projectile contaminates the ground, the plastic from shotshells doesn't degrade, and the lead based priming compounds go everywhere. It is a real nightmare to deal with.
A range is likely better equipped to deal with such an issue and perhaps a collector might want them. Whatever your local policies may be, good luck getting rid of the ammo.