James:
A site to be mentioned when it comes to slow speed diesels and the like is www.utterpower.com [1]. I agree with the site linked – getting one of these small diesel engines is the hardest part in the process. Both the lister types and the small horizontal diesels (made in mainland China) appear on eBay.com [2] from anywhere from $375 to $2000. Shipping is also a bit of a bear due to the high weights; [since] lots of cast iron is used on these. – Rick L.