i would suggest finding a local top & trim shop or a general automotive upholstery place. check your local phone book and ask around the older people in the local car scene. once you find one, talk to them about your custom top ideas.
this isn't something that is regularly discussed here in the vert forum. we've all seen a few custom tops, but none of them (as far as i know) are members here. seems like you're blazing a trail. good luck!
here's the website for my local place. you can contact them if you can't find anyone local for where you are.
http://www.generaltopandtrim.com/index.html
now that i'm thinking about it, once i take the vert out again, i should take it down there and talk to them about getting some work done.