Needing help finding certain utau banks..

To convert USTs between hiragana and romaji, you can use a plugin such as this one.
http://utaforum.net/resources/bizzs-utau-plugins.129/

If you're on Mac and using UTAU-Synth, this will work instead.
http://utaforum.net/resources/romaji-hiragana-ust-converter-for-mac.206/

Generally, CV banks will be aliased to work both ways, while other styles for Japanese (such as VCV and CVVC) are hiragana only.

You can find many voicebanks here on the UTAforum Showcase or over at the UTAU Wiki.

Yamine Renri's website is here, which has downloads for all of her voicebanks.
https://renri-voice.jimdo.com/

In general, most of (but not all) overseas UTAU have a CV VB that are encoded in romaji (a.wav, ka.wav and so on). However, many oversea romaji encoded CV VB has also Hiragana alias: if romaji encoded VB has Hiragana alias, it can also sing in Hiragana UST!

UTAU that are created by Japanese speakers (Ritsu, Teto, Ruko) are exclusively Hiragana encoded and aliased (あ.wav, か.wav), so those sings hiragana UST only.

Like previous person posted, use plug-ins to convert romaji UST to hiragana UST and vice versa, so you can use any VB you wish! Good luck

There is something called presamp. It allows UTAU to render from Romaji CV USTs with Hiragana VCV voicebanks by modifying the input (.bat files) resamplers receive.