Thank you for your helpful comments, as I thought when I wrote the post I do feel better about the situation today than I did yesterday.
I’ve been reading up about Reynolds tubing, pleasantly surprised that they are based only about 20 miles from me in Birmingham. I also read that they did a special run of imperial tubing for the Jaguar XKSS reborn project a couple of years back. I recall that the TV show following the XKSS story hosted by Mark Evans did a short piece at an old school workshop that made up the engine frames for the XKSS.
A few discussions in the pub tonight reminded me that there are still many engineering and specialist short run manufacturing businesses in the Midlands with highly skilled workforces.
I any event I have lots to be getting along with before getting to the point of biting the bullet to cough up the £2,000 plus for replacement frames.
Still open to new suggestions in the interim.
Kind regards all
Nick