Might you consider a used Mercian or Jackson frame?
I have seen some lovely Mercian and Bob Jackson 1970s-1980s frames and bicycles offered for sale in the past several years.
How would you feel about a used frame, with excellent condition original paint, in your preferred size?
The cost of second-hand Mercian and Jackson frames, if one is a careful shopper, can often be less than half the price of a Joe Bell professional paint job.