There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.

Qenya 

semellume

adverb. *a few times, *a few times, seldom

The correlative combinations semellume or sempallume appeared in Demonstrative, Relative, and Correlative Stems (DRC) from 1948 (PE23/110), a combination of ᴹQ. sem(p)- “few” and ᴹQ. -llume “time(s)”.

Neo-Quenya: For purposes of Neo-Quenya I would also use semellume to mean “seldom” to replace (probably abandoned) seman(an).

sempallume

adverb. *a few times

Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.