I would think it's just a matter of return on investment and a relative lack of interest compared to other types. While you Brits may get misty-eyed over certain types, the mention of Vampire or Hunter over here (a huge marketplace) and some other countries might just eleicit a confused "huh?" in response.

I personally would rather see a Hunter (beautiful speed record holder) or Vulcan out at the local field than another 16, but think the Vampire is too ugly and boring for even it's mother to love!

Don't feel too bad about being under-represented though. There are MANY interesting but forgotten American types that aren't offered as kits due to the small potential market. How many of any of the "century series" jets have you seen around? For that matter, I don't see a lot of Mirages either (But I don't miss them, insert favorite French joke here).