OK, found the details.
I did most of my searching through online scrapyards
247spares.co.uk
carparts4less.co.uk
1stchoiceonline.co.uk
breakeryard.co.uk
etc.
of these 1stchoice & breakeryard came up with the most positive replies. Prices ranged from £30 to £80 plus various shipping costs. Although I was getting (almost) desperate I did ignore a couple thet were asking stupid money. You do have to keep trying though. As I said in my first post, good quality subframes are not just lying around anymore. Most probably have the same problems as your current one. ie rotten.
Of the three specialist Fiat breakers I am aware of one has already been mentioned = DA Motors of Wickford in Essex. 01268 767 424. They have a web site and do reply to e-mails. Sadly they didn't have a subframe when I contacted them.
The others are
Salvo 01773 531166
Longridge Lane
Heanor
Derby
Their price was not too bad, and they seemed pretty honest. I had ordered & paid for one but got a 'phone call a day or so later to say they couldn't send it as when removing it from the car they had sheared a bolt and it was stuck in the subframe so it was no longer serviceable. They gave me a full refund but it took a bit of chasing.
The guy who did supply me was...
.... well, I'm not entirely sure of the name of the business. It could be
CarParts UK 0701 312 4346
But direct number to the scrapyard is 0191 237 5951
They are in Seaton Delaval just north of the Tyne in Northumberland.
The guy I dealt with was "Marty". very helpful. very good.
£30 + £15 delivery. Came wrapped in cardboard and although not pristine was extremely sound and in infinitely better condition than the one I took off. Fitting was reasonably straightforward too. All the holes lined up so nothing was too bent.
Just a couple of words of caution if you plan to fit it yourself
1. Have a good set of drills & taps&dies to hand as you will undoubtedly have to remove a sheared bolt or two, and running a tap through all the treads to clean them up makes refitting much easier.
2. Remove the exhaust tunnel heatshield. It will make the job soooooo much easier. I didn't but wish I had.
3. Drop the thing off (& refit) with the suspension arms & ARB still attached to it. They are much easier to remove once the assembly is off the car. You just need to loosen the ball joints from the front hubs and a bracket on the top of the subframe that clips the brake (or is it pas?) lines, then undo the bolts and drop it all down.
4. Have a couple of strong mates and a trolly jack or two to help you. These things can feel pretty heavy with suspension attached when you are lying on your back trying to lift it, hold it, and then get a couple of bolts located before it drops on your head.
Depending how much stuff you break It could be possible to do it in a weekend. I did mine over two, but took the time to clean a lot of stuff up (mainly threads) while it was all apart - drilling sheared bolts out took up a bit of time too.
Good Luck