I read some old posts about other stringed instruments and about possible designs on shamisen. Rather than add my comments, I wanted to share a good online resource. It will help you ID, learn about other instruments, and imagine traveling along the Silk Road. For example, besides the Chinese sanxian, Okinawan sanshin, you can find 3-stringed lutes in S.E. Asia, Central Asia, Middle East, and so on. The site has pictures, description, and on the left sometimes links to YouTube or other websites for more info.
Atlas of Plucked Instruments
http://www.atlasofpluckedinstruments.com/
Also, I bumped into a website recently called Far Side Radio / Far Side Music. Real interesting music he sells and can ship internationally. But I am having a lot of fun listening to archives of past radio broadcasts. Give it a listen! (You can go forward but not backwards. If you want to skip the show’s intro, jump fwd about 2.5mins.) Real eclectic stuff and each show has a different theme, so pick a topic you like and see. Sometimes artists are live in the studio, so he has variety. The playlist is also shown, to give credit to musicians and their albums.