Thanks for the link to the ForMatKonaVe font. I've downloaded it and the readme says:

ライセンス
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この作品は、クリエイティブ・コモンズの帰属-同一条件許諾（Creative Commons Attribution-ShareAlike） 2.5ライセンスの下でライセンスされています。
この使用許諾条件を見るには、

http://creativecommons.org/licenses/by-sa/2.5/
http://creativecommons.org/licenses/by-sa/2.5/deed.ja

をチェックするか、クリエイティブ･コモンズに郵便にてお問い合わせください。
住所は：559 Nathan Abbott Way, Stanford, California 94305, USA です。
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これは元にした小夏フォントと同じライセンスです。


So, according to Google translate, the font is under the same creative commons license as Konatsu and I think I could use that.

I will try out if it works with Textastic and if it does, I will add it in an update.

The following scripts are supported:

• Latin (including European and African alphabets, IPA, ...)
• Greek (including polytonic)
• Cyrillic
• Armenian
• Georgian

Following scripts aren't available in all the styles:

• Hebrew
• N'ko
• Tifinagh
• Lao
• Canadian Aboriginal Syllabics
• Ogham
• Arabic

Apple seems to have the copyright for the Monaco and Menlo fonts and unfortunately, they are not included with iOS.

I asked Apple several months ago if I could use the fonts in Textastic, but after they referred me to their legal department I never got an answer.