Found the old thread :-
There's a few places that will do a good repair of diamond cut Monzas - A1 Wheels in Wolverhampton being one - there's plenty of happy Mk 5 Gti owners had theirs refurbished there. They can do this too :

Paint the insides black on older Mk 5 Monzas and then cut back and refurb the diamond cut face
Other places that used to refurb them are (taken from another thread

) :-
Rimfurbish
http://www.rimfurbish.co.uk/index.html0121 525 2525
Matt Ball
£70 + VAT per wheel
£7.50 + VAT per wheel to strip and refit tyres
£30 + VAT total shipping (all journeys)
Lepsons
http://www.lepsons.com/home.phtml01634 580582
£68 + VAT per wheel - 7 working days
£90 + VAT per wheel - Leave whole vehicle, 2 working days, booked solid for several weeks
Have samples in their showroom to decide whether their Diamond Cut is close enough to the existing wheels
Spit & Polish
http://www.spitandpolish.co.uk/01732 367771
£62 + VAT per wheel - 5 working days, or leave whole vehicle, 1.5 working days, booked solid for several weeks
Pristine Alloy Wheel Refurbishers
http://www.pristinealloywheels.co.uk/01908 282628