I can't remember seeing a dilute draft stud advertised anywhere, certainly not a purebred one at any rate so if you found one it would probably be a cross and to me that probably wouldn't be the best route to go down if you're trying to work towards a Sugarbush. I have seen a couple of dilute Gypsy stallions but one is a tobiano and the other is below the height you want. I'd vote the same way as the others, go back to a Percheron if they were used in the original make up of the breed because you're more likely to end up with a foal more along the lines of what you want. Breeding your filly to a Knabstrupper to me wouldn't be the best idea because it's not a draft breed. I may have read who was to breed to the Knabstrupper wrong and it was the filly's dam you want to breed to the Knabstrupper.
I did find someone else who describes themselves as a breeder who said they would love to get access to a Noriker as they are a purebred spotted/variable coloured draft established over hundreds of years.
I did find a US appaloosa coloured Gypsy Vanner (as they are called here) and these larger gypsy type horses do come in all colours in the UK so shouldnt be ruled out as a possible as I'm sure someone must 'stand' one in the UK somewhere