If he has D1 interest and I'm presuming he is a junior so you can freely communicate with colleges so that's good. You don't need an agent for that. Now if he is a repeat that might be the reason there isn't as much going on agent wise because he's draft eligible next year and probably not on any radar or scouting lists.
Anyway, there was an artical in NEHJ some time back on the most influential people in NE hockey. In that artical are a few agents mentioned. Matt Keater, Kent Hughes and Peter Fish. I would reach out to them. I'm sure if you are resourceful you can get their contact information. Ask them to take a look at your kid and ask for feedback. If they like what they see they will gladly be your kids "advisor". If he really doesn't project to them as an NHL player then at least you know. But I'd say at this point that if you have Hockey East schools reaching out then they would be interested. It costs them nothing and if your kids a late bloomer then they win down the road.
In terms of USHL I would wait till next year. Going out there this late is not a good scenario. If he makes a team he is probably a 4th liner. If he's cut then it's very disruptive to the school year. Just not a lot of upside to trying to make the jump at this time. If he's a D1 kid he'll be drafted in the spring and then you have time to investigate options.