Check the public notice listings for the Star Ledger or the NJ.com site. All county & municipal equipment must be disposed of at public auction & these auctions must be advertised. Most towns use one of the two places I listed to advertise. You may want to try Googling municipal auctions & NJ, but you may get too much BS. Also you will find better deals at towns that do their own auctions as compared to those who hire auction companies.
Happy hunting,
Ed