A couple of years ago I did a presentation on "crapppy" lenses for my camera club. I researched for half a year and began buying what were said to be "bad" lenses. What I found out is really, there aren't any bad lenses, at least not in the artistic sense. The historical lenses I've been buying were all actually state of art when made, and are still quite good in their own way. However, keep this in mind. From roughly 1840 to 1905, lenses were made only for large format. Up until the 1880s, when rapid rectilinear lenses became smaller, most lenses started with the 6 inch (150mm) focal length, and those were made for quarter plate. There were a few smaller lenses made for even smaller amateur cameras, but those are pretty rare. There were also some shorter focal lenses made for stereo cameras. In the first decade of the 20th C. roll film appeared, smaller cameras were made and those have shorter lenses. However, lenses for 35mm format still didn't exist in any numbers until the 1930s, and those were anastigmats made by premium manufacturers such as Leica and Zeiss (Contax.) This brings us to World War 2, which turned the lens business upside down. At the conclusion of the war the German patents (DRP) were ruled invalid, and many countries began making cameras & lenses that were previously owned by German makers. Soviet Russia actually dismantled entire German factories and moved them (and employees) to Russia in the 1940s! Many of those Russian lenses are.........interesting.
I think for what you're wanting there are four categories of lenses to begin researching:
1. Historical lenses. Small ones appear from time to time, but these can sell for surprising money. I'm not the only one who likes to mount these on modern cameras!
2. Post War copies, such as the Russian lenses. I strongly suggest you research the Helios 44-2 to start. It's 58mm and in 42mm screw mount. Easy to find on ebay. There are other Russian lenses that would work for you as well. Some of the Italian lenses were kind of funky too, but those get expensive.
3. Novelty lenses. These include the Holga lens that you can buy from ebay for about twenty bucks. However, it's practically useless and not all that fun. Another thought is to buy a pinhole lens cap. Now those ARE fun to use! My favorite of the novelty lenses is the Sima 100mm. It's a plastic tube with plastic element. Can be found for ~$20 on ebay. Another of the cheap Post War lenses is the Hanimar Hanimex 28mm, available in 42mm screw mount. Finally, Nikon made a set of plastic lenses about 20 years ago. These were sold in 1996 (Nikon Amusing Lenses) and again in 2000 (Nikon Fun Fun Lens Set). They can be found on ebay, of course. They are interesting. Available are 20mm fisheye, 90mm, 120mm macro, and 400mm telephoto. The results are similar to the Sima 100mm.
4. Cine lenses. These were made from 1900--1940, uncoated, and include many Petzvals. I don't have any experience with them personally, but they are for the smaller 35mm format. I don't think they have a way to focus, so you'd need a helicoid or something to achieve focus. SK Grimes can make them.
Anyway, to conclude, no lenses are truly bad if used in a way that creates your artistic vision. My favorites of the genre are a pinhole body cap, the Sima 100mm, and Helios 44-2.
Kent in SD