Welcome to the forum Fusion
Here are two AWS Accredited test facilities...
Triangle Engineering, Inc.
6 Industrial Way
Hanover MA 02339
Plumbers Local No. 12
1240 Massachusetts Ave
Boston MA 02125
But to really give you a good answer we must know what type of cert you are looking for... Which code, which processes etc...
There are community and technical colleges in your region that may also be able to certify a performance test.
The easiest way to go however is to have your employer worry about certifying you... Most certs don't travel anyhow... They may get you in the door but any employer worth their salt is going to test you again anyhow.