If they spot it, your bike will be failed. If the leak isn’t too bad and you’re prepared to live with it for a little while, then stop a short distance before the MOT station and wipe the fork stanchion and leg with a tissue or rag. If you’ve got dust covers at where the stanchion enters the leg, then make sure that you pull up the cover and wipe in there too. I’ve done this with older bikes and it works a treat every time!
A leaking fork seal is a def fail and they shoukld spot it unless you do the wipe down bit. If your forg legs are pitted, you can get them rechromed as opposed to sourcing new/second hand parts. If you strip the forks down and get them to a chromers, they should be able to redo them. A new set of fork seals, the correct oil etc and the front should be pretty good.
Suggest you look through yellow pages. They are not that common but they are about. Maybe worth finding a shop that deals with classic bikes, they are bound to know of someone.
Go to newsagent and have a look at the back of MCN paper. There will be chroming places in there for forks specifically. Lots of breakers too! £1-70 and you’ve a decent enough directory for bike bits.