As lunde indicated it's a bit of a tough nut to find a .40 P99 barrel these days. About the only folks I knew of making them were Jarvis and Bar Sto. Of those, Jarvis has taken their P99 barrels off their product page... Jarvis still shows the 9mm version. It's a long shot, but you could contact them to see what they may have in old stock. An even longer shot would be to contact the folks at AAC and see if they have any leads on the .40 barrel you want.