While I'm not a realtor, I get a lot of buyers moving from NYC and many of them are finding me from my website.  So you may want to dial that up.  Maybe write some articles about life in Orange vs. the City and commuting times.

If I were you, I would look to create some strong relationsships w/ NYC realtors, as they can refer biz to you.

The other thing I would do is try to see what other realtors in Westchester, LI, other parts of NJ (i.e. other suburbs but not competing w/ you) and see what some of them are doing to get this biz. 

Your best bet would be to cultivate relationships with NY realtors - I can tell you that I fairly frequently have buyers who decide they'd rather not live in Orange County but would like to move to NJ instead.  I'm sure there are those in Rockland and Westchester who find the same.

Localism posts

Write tons of neighborhood blog posts, those who are planning to move will find you while doing their research.

use a variety of keyword phrases that new yorks who are moving to new jersey may use when they are searching online for an agent to work with.... that's the only way you'll target them....make your keyword phrases what one of the potential buyers would search for....

Have not done it long enough, but I have a few Facebook Ad campaigns going targeting California residents that are looking to buy in Las Vegas. I've been getting some traffic, but it's to early to tell if it will be a good ROI, it's a pretty broad target so not that easy.

Facebook has really good targeting adds that can pinpoint many items such as location, age, sex, income level, education...

There are some great suggestions here already. You might also want to start doing posts. Something like...what you need to know if you are relocating from NY to New Jersey. Use keywords that those relocating might be using to search for information. 

Kat Palmiotti nailed this one...

One paid online marketing idea would be to geo-target people in New York performing keyword searches such as "relocation to New Jersey", "NJ relocation", "New York to New Jersey movers", etc..   You can do this with both Google Adwords and Bing Advertising.  Send the traffic to a landing "squeeze" page that has strong calls to action and that shows you as the NY to NJ relocation expert.  Consider writing a short relocation guide that visitors to your site can download in exchange for their email.   

When I am looking for a buyer from out of town and know where to look I post my blogs in that city and state here in ActiveRain.

You should be able to purchase mailing lists for apartment buildings but I do not know if it would be worth the investment for the small percentage that will move to your area.

Perhaps put some type of ad on your car, noting relocation specialist for your area?