Stephen,
Do you know anything about Maker Faires? The flagship faire is coming up in the San Francisco Bay Area in May and I think your amp kits would be a
big hit. This event draws displays, vendors and attendees from all over the world. There is a very strong correlation with the maker movement and all things music and electronics, especially anything that is "retro". Tube amps and makers go hand in hand.
I went to last year's event and there were a lot of music themed displays and vendor booths but none for tube amp kits.
I am even half considering doing a non-vendor display booth of my tube amp builds and inviting a few other California builders to do the same just to draw attention to the hobby.
Anyways, check it out... i think it would be great exposure for your awesome kits! 120,000 people attended last year's event.
http://makerfaire.com/