How does one find an advisor doing research on a niche interdiscipinary subject?
From my perspective (as an advisor), you sound like the ideal candidate: someone who is self-driven and motivated to work outside the regular comfort zones.
Assuming you can't find anyone at the exact intersection you're looking for, my advice would be to find a potential advisor who values interdisciplinary science like you do, and works in one or more of the disciplines involved. I would start by asking the most relevant faculty at your current university if they might know of someone who fits the bill that you could email.
For an advisor that values interdisciplinarity, your background shouldn't matter so much - they will be looking for initiative, drive, and decent grades. Argue those three things as concisely as you can when you send those emails.