[Xx{Midday}xX]

I only know of what's in the touhou wiki.

http://touhou.wikia.com/wiki/Seihou

But yeah, I would like to know more about the game too.
homepage: http://ss-do.hp.infoseek.co.jp/index.html

It looks like doujinstyle doesn't have anything earlier than this, unfortunately.
(game3 full) Banshiryuu: http://www.doujinstyle.com/doujinsoft/banshiryuu.php

(Not official Seihou) Samidare: http://www.doujinstyle.com/doujinsoft/samidare.php

Trials/Updates are here. Not sure if doujinstyle has them updated.

Shousougyoku game1) http://ss-do.hp.infoseek.co.jp/saku/....html#download
Kiougyoku game2) http://ss-do.hp.infoseek.co.jp/saku/....html#download
Banshirryuu game3) http://ss-do.hp.infoseek.co.jp/saku/...l#download_upd
Matemate Question Gaiden gameextra) http://ss-do.hp.infoseek.co.jp/saku/....html#download

Seihou music sucks hands down. Samidare was ok, but it's not part of Seihou.