Ask the local building department. They know who is good.. Or ask local Realtors for a referral. If you are replacing plumbing, use a licensed master plumber.
I've used Homeadvisor.com. At least you have reviews and you can vet them. hope that helps.
I have had pretty good luck with Thumbtack. Just get several bids. You are going to have a hard time because it is such a small job, contractors wont want to waste time or money on it if they aren't sure you are serious about hiring them. A licensed plumber will typically run you 150-300/hr plus the cost of the toilet. Maybe more in NJ.
As Vanessa mentioned, I would check out homeadvisor.com since they have reviews and you can compare costs! Good luck!
I've found great people using facebook. Ask your friends who are local who they would recommend. You'd be surprised. Everyone lives somewhere, and most have had to hire people to fix things on their own home.