I second Lionel Hering as a very skilled bootfitter. He does some retail, with a limited line. Lange Dealer, perhaps Salomon. My suggestion as a first stop would also be Ski Depot, in Jay. Check on line for brand selection. Jay is about an hour south of Sugarloaf, about an hour and a half from Portland, and 45 minutes to Sunday River. The brands and selection, I think are identical at The Boyne owned mountain shops at both Sugarloaf and Sunday River. At Sunday River, you also have Jack Frost. In the Portland area, you have SnowConnect {the former Joe Jones}, and Arlberg. North Conway, NH has a lot of options....an hour or so from Sunday River. Stan and Dan is a very good shop. Joe Jones is there. Newfy, I'm not sure how much Poulin's is doing ski business. I think primarily a bike shop these days. Al's is on-line, but the owner has been known in the past to meet people at his "barn" to help them out. He's in the Freeeport/Yarmouth area. Good guy.
I might head to Jay and Ski Depot, and then if needed, to Sunday River, and maybe even North Conway. There's no one shop that will have it all. Ski Depot is a dealer for about 6 major brands of boots, though. Nordica, Fischer, Lange. Atomic, technica, and I think Dalbello.
You also need to call {not just check on line} to check on hours of operation for these shops this time of year. The mountain shops, in particular.
Good luck.