Websites such as Car-Part.com allow people to search for car parts, including full engines, located near a particular ZIP code. TheAutoChannel.com lists parts near where the user searches, so people searching from Wisconsin see parts close to them at the top of the results.
Another option is checking Craigslist. While the website is more popular for full vehicles, sellers sometimes share large parts, such as engines, on the website. Newspaper classified sections might list parts as well, and some sellers who sell expensive car parts might list advertisements for their business in classified sections.
Scrapyards also sell parts, and many scrapyards have a searchable database of parts in stock. Drivers can call various scrapyards and ask if the desired engine is in stock. However, scrapyards generally don't provide any guarantees on the parts they sell, so it's worth having an expert look at the engine before you purchase it.
Drivers looking to save even more money might want to consider junkyards, which typically don't categorize their parts and require buyers to remove the parts themselves. Like at scrap yards, junkyard prices vary considerably, but drivers looking to save money can often find a great deal. Check the engine out first, and make sure another buyer hasn't removed critical components.