I bought headlamp bowls, complete with mounting rings etc (everything bar the sealed beam unit) for a rover mini from my local lucas stockist. Fitted a mk1 fine, although the gasket is not the same, with the mini one a lucas part and the cortina one a ford part. This was about 11 years ago when the headlamp bowls were about £25 each, but I am sure these mini ones are still available.
Tommy