Here is the Definition of numeral:
noun: a figure, symbol, or group of figures or symbols denoting a
number. a word expressing a number.
adjective: of or denoting a
So, it be wrong to use a past tense of numeral. And have a look at this ngram which suggests that Roman numbered, or Roman numeraled don't really have any appearances in books (agreeing to what you found out).
So I would rather go along what @gmcgath suggests and use an alternative like:
- the book uses sections numbered in Roman numerals.
- the book uses sections with Roman numerals.
- the book uses sections divided (grouped) into Roman numerals.