A few months ago I saw ad in the Star-Ledger about plant sale from garden club in your area. Try to call township recreation department. Usually they know everything. Or try a library, sometimes it has a lot of notes on walls.

Try the link below

Here is a link that might be useful: Skylands area Garden Clubs

I'm in the Montgomery area also. there is a garden club out in west Hillsborough, in Neshanic Station. I've heard of the Stony Brook club which worked on the Rockingham gardens - Stony Brook implies Hopewell Twp.

there is a garden club in Princeton but it is by invitation only. it seems to be a rich ladies' charity organization.