There is someone here in the US who is or was reproducing some of the window rubbers. I'll try to dig around and see if I can find his contact info. That choke knob, and the others on the dash, are made of the usual unobtanium. It's possible someone in or connected with The Mayflower Club is reproducing knobs, though.
And that club is pretty much your best bet for most bits. I've not been able to maintain my membership over the years, but they were invaluable back when I first got my Mayflower and was determined to get it on the road (which I did, for several years, until minor mechanical problems as well as family situations got in the way, and the car got stored).
If you're interested, I'd like to list your car on my Database page (URL in .sig file below). There is also a small but dedicated (and, as you might expect, low-traffic) e-mail list for Mayflower owners (not to take anything away from this forum, of course). Details are on my web site.
BTW, my car (in better days) is pictured on the VTR web site. It is TT22461LDL, one of the 500 or so "officially" imported by Fergus Motors of New York City for the US market.