Your circumstances are confusing. When you say "transferred to an FFL and brought into the state" do you mean transfer to an out-of-state FFL and then you traveling there and then bringing it back here? If that's the case, the vendor is correct - you need to have the lower sent to an in-state FFL for transfer to you. A frame or receiver is considered by the BATFE to be "Other Firearms" and not transferable to a non-FFL out of state. This isn't a Massachusetts thing, it's a federal thing.
If you are a MA resident, you should be able to purchase a stripped lower from out of state and have it sent to your MA FFL for transfer to you. By the time you add in shipping and transfer fees, you're probably over the cost of buying one locally. The election was a long time ago and there are currently plenty of reasonably priced lowers to be found at your favorite dealer...as cshooter said above, why not reach out to John at Remsport and see what he can set up for you?
(edit: replied at the same time. If you have a local FFL, you should be able to send a copy of his license to the seller and have the lower sent there. Your local FFL will then transfer to you. Talk to your dealer first to make sure it's cool with him.)