Disney owns the show now, so good luck.

It was part of the MTM library, which was badly mistreated before Fox bought it. First it was purchased by a British company, then religious huckster Pat Robertson. The original elements were not treated kindly before Fox bought MTM in the late 90s.

When Shout Factory released the series on DVD, they had to use ancient videotape masters, and even resort to pulling YouTube quality clips to reinsert into some episodes to make them as complete as they could get them.

So, Newhart would have to get the TNG/Cheers/Frasier remaster and reassembly treatment to look as good as it could again, and Disney... well, they're not known for that sort of thing the way Paramount is. And that's assuming the original film still exists and is accessible after all the hands it passed through over the years.