I'm not even sure if there is much of a commercial market for Touhou outside Japan or the Asiatic region. Out of curiosity, and after reading this post, I went onto Google trends to see what would pop up if I typed in "touhou". While it looks like Touhou is steadily growing more popular every year, searches for Touhou are popular predominantly in the the Asiatic region (especially Singapore, Thailand, and not surprisingly Japan).
I used the English version of Google Trends though and I'm not sure if there exists something similar that can search for Touhou trends across multiple search engines, languages or regions. Any thoughts or ideas?