Weber 36 TLP Jets

I own a 1982 1.5 auto cabriolet fitted with a weber 36 TLP carb. The problem is the car drinks petrol in an alarming fashion (less than 20mpg).
Have checked for fuel leaks so no problem there.
Come MOT time it always struggles to get through the emissions test usually passes by messing with idle mixture screw.
I was going to try some different jets but can't find anyone who stocks them.
Can find jets for every other weber carb except the 36 TLP.   :cry:
Anyone got any suggestions.