Jan offers good advice and Rog's webpage is full on awesome, so do spend some time there!
One of the nice thing about Jensen engines is that even after almost 90 years, they are still a family owned business and will supply parts for the engines that they have made, with but very few exceptions of some of the really rare or old ones. Parts for yours will not be a problem!
You'll find them here:
http://www.jensensteamengines.com/parts.htm