There are several vendors of parts in North America. In the USA, there’s Diesel Electric, and if you are on the East coast, Central Maine Diesel.
Diesel Electric (Kansas and Alaska) has been working hard to stock parts for a variety of reliable Diesel Generator plants and Engines. There are two or more active dealers in Canada, and one selling the famous Air Compressor used in India, it is built exactly like the Diesel Engine, you just move a few parts and add an injector, you become the builder of an engine should there be any EPA rules or regs, you are on the hook, not the seller.
As of this month, I have found that some sellers do show up on eBay, and now I see that some of the Indian Companies are offering parts directly from India for a flat shipping fee. No doubt, they have seen the success of the Chinese doing very much the same, only the Indians have not yet been able to engineer a method to make the shipping costs as reasonable.
If you consider ordering engines directly from India, consider that they need to be parts or kits, completed ‘engines’ must meet emissions standards, and as you know, many DIYers build Co-Gen power plants with emissions added. Indian air compressors contain many of the same parts, and have no emission standards to meet, so the guy in the Customs office is going to have far less to check for compliance. Do understand that all I say here need be verified, as I only repeat stories on the WEB, but don’t we know it must be true, or it wouldn’t be allowed on the WEB!
Lovson Company in India is one company that has proven over time that they are there to support you when you need parts, or you have problems. When you open this link, note the air compressor in the lower RH corner of ‘engine’ images. They sell the Indian air compressor and you can order a parts kit that has all you need to build that CO-GEN power plant you wanted to build. you might check on import duties as well, in your country, which is cheaper to import, Air compressors or engine parts? Maybe it will influence whether you build one or the other?