I just happened to find links to 4 “ancient” Japanese Go books on GoDiscussions.com, viewable online and downloadable as PDFs. Even though they are Japanese you can still get the idea behind them as pretty much all of the pages contain all kind of Tsumego. Just click on the respective pictures in the links to get to the download-links.
- Igo Myoden by Inoue Inseki (囲碁妙伝. 巻1-4 井上因碩)
- Kokugi Kanko by Honinbo Jowa (国技観光. 巻1-4 本因坊丈和)
- Ekisei Tsubiho by Yo Kisei (expanded by Saito Masatsugu) (奕正通微補. 雍 熙世, 斎藤正次 増補)
- Gokyo Seimyo by Hayashi Genbi (碁經精妙 Gokyō Seimyō, Best of the Go Classics)
Hope you like it!