Are you near Rte 130?

There are a few on Rte 130, if that is in your neighborhood:
1. Amato's Garden Center Nursery & Landscaping - (732) 297-6904 - Us Highway 130 & Deans-rhode, Monmouth Junction, NJ

and crossroads-
http://www.crossroadsnursery.com/directions.html
in south brunswick.

They both have a large quantity, but of the usual common annuals and perenniels, nothing out of the ordinary.

If you want to go a little further afield, I suggest a trip to Somerset County, which has a lot of nurseries. And my favorite NJ garden center is Ambleside.

and if you want to take a drive toward Princeton, on Rte 27, there are a few nurseries along the way.

You might also try Gasko's in Monroe Township, Molzon's in Lincroft or Colonial on Front Street in Red Bank. There is also a new(ish) place in Colts Neck on Rt 34 South at Roberts Road (north of Rt 520), I don't remember the name, but it looked like they had a good variety.

Here is a link that might be useful: Gasko's Family Farm

Diane beat me to it.
I LOVE Gasko's in Monroe too, lots of selection, good prices. Everything I've ever gotten there was healthy too.