Pedersoli makes some nice flintlock Kentucky rifle kits. This one is .45 cal, but they've also got it in 32 and 50. I like the .45 myself because it was historically a popular caliber for longrifles and it's big enough for close up work on deer but not too big for small game. I know you said it's gonna be a showpiece but you never know... someone might catch the fever and decide to use it someday.

http://www.dixiegunworks.com/product_info.php?cPath=22_162_193&products_id= 2028