By that I assume they mean made to measure.
And by that you assume wrong.
The only thing that matters for the movie is how it looks on screen. How close do you have to look to distinguish a made-to-measure suit from an off-the-shelf suit tailored to fit? The camera really isn't going to be that close.
And that tailored to fit part. How long does the tailoring have to survive? Answer: one day's filming. The wardrobe department have staff who can quickly measure a person and tack-stitch their costume to fit. Or in some cases literally sew the person into their costume. (Historically that's how women put on elaborate gowns, after all.)
Sure, some costumes need to do better than that. Or the producers choose to let the wardrobe department and actors collaborate to get something which helps them get in character. The wardrobe department on LotR spent significant time making outfits and equipment which worked practically, especially for Viggo Mortensen who went full-method-actor and actually spent time camping out in full costume. This was a long-haul filming process over 3-4 years though which is highly unusual; and even with that, they recognised they were overdoing it, but with fanboy producers and directors they were allowed way more scope than usual. And yes, the wardrobe department did genuinely make everything from scratch, because Ngila Dickson is an artist.
As for your claim that there are no tailors in New England, let me google that for you with a search for "bespoke suit boston". I'm not going to waste more of my time searching other New England locations.