Is there a reason none of the nurseries are suitable? I know back east, many retail garden centers/nurseries offer garden design as part of their services. You would want to evaluate them the same as you would any independent designer - completed work, pricing, any purchase restrictions (like their plants only), client rapport, etc.

Otherwise, I'd suggest you contact the New Jersey chapter of the Association of Professional Landscape Designers. This is as close to a certifying body one is going to get with a designer and their members tend to be highly skilled and experienced. Design-only or DIY clients should be part of their scope but not necessarily for every designer. You may have to call a few :-)

Here is a link that might be useful: APLD - New Jersey

Thanks. Good info. I will get in touch with a few of them. I have a half acre plot and I would like advice on most of it. What would a plan for that size lot typically cost?

re: price, it depends. Depends on the designer, depends on the scope of work, depends on the complexity of the site, depends on what you get at presentation, etc., etc.

APLD is a great resource. Sometimes your local stone yard has a designer or two they recommend as well.

Check out Rutgers Landscape and Nursery in Ringoes. They are in the process of doing a plan for my 1+ acre.

I think Houzz also has listings of professionals by area.