Also there's ski ward in MA. They have an airbag open and a small run with a few rails set up generally. I think that's about it in the Northeast at the moment.
As mentioned there is a place called ski ward in Shrewsbury, MA (10 minute drive for me, score!) and they generally have 7-8 rails set up and a pretty good airbag but it's relatively small place. Only other place I know of is Liberty but I heard talk of a place opening up in Boston within 12 months here is the link to the thread they made about it: https://www.newschoolers.com/forum/thread/785707/Indoor-Skiing-in-New-England
IMO it's too bad there aren't more snowflex places in this area.