rabagley, welcome to the forum.
The diesels that are based on the old British designs are made in India (i'm sure that some are made in China also),
http://www.utterpower.com/Lister%206/1.htmIf you are looking to build your own there is a lot of good information on this site.
The "China Diesels" are based on a German design, if i remember correctly. From what i understand the build quality of these units is poor and you might make it to a few hundred hours before a major mechanical malfunction happens. Have lots of spares and know how to work on it.
The India made engines don't have a stellar reputation either. These are the engines can be torn down and put back together in an afternoon. And you still need to have lots of spares and know how to work on it.
If you are looking for an diesel that parts are available though the US one of the Detroit diesel refer generators might be the way to go. Here are a couple of sites,
http://www.green-trust.org/wiki/index.php?title=Green-Trust_Heat_%26_Power_System
http://stores.ebay.com/AFFORDABLE-POWERDisclaimer, i have no affiliation with any of the above web sites and this is presented for information purposes only.
If you like working on and playing with engines, one of these would be a wonderful toy. But if you want a small reliable diesel generator i would go for an Onan or one of the welder/generators mentioned by Reddog.