I've recently become quite interested in the trial versions of Touhou and Seihou. Various trials seem to have some interesting differences that didn't make the final cut, such as with Touhou 7's (Perfect Cherry Blossom's) character portraits and spell cards, so I like to think of them as betas in a sense.

https://tcrf.net/Proto:Touhou_Youyoumu:_Perfect_Cherry_Blossom

I'm currently in the process of collecting and archiving some event-distributed (Reitaisai and etc.) trials; I've snagged Touhou 11's (Subterranean Animism's) recently, but my goal is to retrieve and archive the event-distributed trials of 8 (Imperishable Night, nightmarish to obtain as listings are rare and often go for $200+), 9 (Phantasmagoria of Flower View, mostly cheaper and less painful to get at $50-$80), 10 (Mountain of Faith, usually easy and cheap at $10-$20), and 11 (Subterranean Animism, currently on the way). I might focus on some of the fighting game/spinoff trials later. I'm surprised nearly no one has archived these... I'm guessing it's because people in Japan seem not to like redistributing copyrighted material of any sort along with these trials being relatively obscure in the west.

Most of the newer Touhou trials can be found on Steam. Touhou 15 (Legacy of Lunatic Kingdom) and 18 (Unconnected Marketeers) are the only newer games as of now with event-distributed trials not on Steam or archived yet.

I've seen quite a few really obscure web trials, such as Touhou 7 0.07, 0.08e, 0.09, etc. on the blog https://touhou-memories.com... I've tried inquiring about these trials to no avail. However, I have seen quite a few Japanese magazines with Touhou and Seihou trials, such as TechWin and DOS/V Power Report, so I'm guessing they're from some of those and that I need to look harder. I'll see if I can get my hands on some of those and archive them.

TechWin issues have had some notable Touhou and Seihou trials, as stated by a Japanese blog post (https://onasu-1341.hateblo.jp/entry/2022/06/26/050554):

September 2001 - Seihou 1 (Shuusou Gyoku) 1.00h (Probably one of the trials already on Wayback)

March 2002 - Seihou 2 (Kioh Gyoku) 1.208 (Probably one of the trials already on Wayback)

November 2002 - Touhou 6 (Embodiment of Scarlet Devil) 0.13 (Latest trial, still hosted on ZUN's site)

March 2003 - Seihou 3 (Banshiryuu) 0.01 

July 2003 - Touhou 7 0.08e

August 2003 - Seihou 3 0.04

Some Seihou web trials since they were a bit of a pain to find on Wayback:

Seihou 1 1.00h(?): http://web.archive.org/web/20050615211524/http://ss-do.hp.infoseek.co.jp/saku/file/ssg/ss1205.lzh

Seihou 2 1.208: http://web.archive.org/web/20020316225332/http://isweb6.infoseek.co.jp/play/few/KIOH1208.LZH

Update:

I finally got my hands on those TechWin magazines with unarchived trials. Enjoy the archives!

https://archive.org/details/techwin-march-2003

https://archive.org/details/techwin-july-2003

https://archive.org/details/techwin-august-2003

Update II:

I and some others were able to get some more of the Reitaisai 0.01a trials archived recently! Here are the Touhou 9, 10, 11, and 15 trials for your enjoyment:

https://archive.org/details/th09_001a

https://archive.org/details/th10_001a

https://archive.org/details/th11_001a

https://archive.org/details/th15_001a

Update III:

I have just archived Touhou 18's 0.01a trial! Only one mainline trial disc--Touhou 8 0.01--is left to find and purchase, but I may also start working on archiving the spinoff trials some time soon.

https://archive.org/details/th18_001a

Update IV:

It finally happened. Touhou reverse engineer zero318 has dumped the Touhou 8 0.01 trial!! Here it is:

https://archive.org/details/eiya_001

Guess it's now time to focus on Seihou and spinoffs... 

I’ll be posting my findings and archives here in this post over time. Check back and check them out if you’re interested!