I understand your position, can't you get a new flue from the makers? Without a correctly installed and suitable flue, the boiler is useless, if you want it to operate within the set safety standards. Have you tried looking on E Bay for a flue?
I just took a look on E Bay, their are a few, take a look.
Well they say they are absolute which is strange really when it’s just two bits of tube with one inside the other.
Can’t find the specific one for it anywhere so I’ll probably end up making one up…