I need a libretto

You are better off looking for a librettist, one which will work closely with you and has the same goals, sentiments, interpretation, etc as you.

If you have writing skills, you (or a librettist) can pull a satisfactory (even superlative) libretto out of a public domain (or original) play, poem, story or novel. If you study libretti, by da Ponte or anyone else up to modern times, you can get the idea of how to do this. There is likely help available online.

I've used online courses to gather in such interpretations of poems and other works, or to extract a scenario.

On the .com site enter "lyrics" in search. You will find people who write lyrics. There are those in their bios who claim to write lyrics, poems and plays. I've noticed plenty of collaborations on the site. You may find someone there.

That's the best I can do.

PS I see you had joined C&F group. You should post the mass there...a good place for a WIP. I recommended @BSG take a look, but you have to post it there, especially if you get involved with counterpoint in that style. My own observation is that it sounds good, but the people there live in that era and know it more intimately.

Judging from what I've heard, the collaboration with lyrics may be a good idea for you.

Good luck.