Over here you're try Dave Clarke Racing, Midwest and Trevor Popes for the plastics or obviously ebay.
For graphics you can go Blackbird (bit bland), all sorts of custom ones on ebay or see if you can some made up by danger-uk or similar.
I'm not sure why main dealers woukld be recommended as they will only sell you OEM stuff and you can't get OEM decals for that age now.
DCR is out of them now.
Danger UK will cost you well over £100 for a bespoke set. nearer £125.
The Blackbird aren't inspiring but I always think new uninspiring beats crap plastic naked dull everytime!
I do the Blackbird kits and you might also consider the three race number backgrounds as another 'patch'. red looks good and so does black. yellow is standard and harks back to the OEM colours.
I've seen pictures of all-white KTMs, as in white plastics. From about that era IIRC. How much of the plastics cross over? Fender, headlight ... what about the rear end?
the pure white would look so clean cut .. i may go down the route of dying the plastic pigments, i looked into this before with a vintage mx bike i had.
heres the frame so far... and yh if you have that file it would be appreciated.
Here's the EPS file. I was about to use it to make some decals for mine, but haven't printed them yet, so bear in mind there may be little adjustments needed.