A Quenya prefix for “a great number, host, very many” appearing in Demonstrative, Relative, and Correlative Stems (DRC) from 1948 (PE23/100). In this document, it was derived from the root ᴹ√SRĬMĬ, but this was revised to ᴹ√RĬMĬ, though this change was not reflected in other words from this document (PE23/100 note #34).
Neo-Quenya: For purposes of Neo-Quenya, I would assume the prefix for “(very) many” is ᴺQ. rim-, since that is consistent with the forms of the root both before and after 1948.
The correlative ᴹQ. hrimindon appeared in Demonstrative, Relative, and Correlative Stems (DRC) from 1948 (PE23/111), a combination of ᴹQ. hrim- “many” and the similative suffix -ndon.