The "final" "final" Kenshin OVA is being released 
right now. Its available on DVD.

Follow the link for a preview.
http://www.sonymusic.co.jp/Movie/TV/Kenshin/seisou
/movie/index.html

A few cels have crept up on Yahoo Japan and 
Usagis had one on Ebay. The art looks very nice 
but I'm waiting to watch the end of the TV series 
first since it apparant picks up from there.