עמוס ז:יד
וַיַּ֤עַן עָמוֹס֙ וַיֹּ֣אמֶר אֶל־אֲמַצְיָ֔ה לֹא־נָבִ֣יא אָנֹ֔כִי וְלֹ֥א בֶן־נָבִ֖יא אָנֹ֑כִי כִּֽי־בוֹקֵ֥ר אָנֹ֖כִי וּבוֹלֵ֥ס שִׁקְמִֽים:

 בלס appears only here in TaNa”KH.

Incidentally, the 1906 Jewish Encyclopedia has a full list of Hapax Legomena.

HALOT connects the word to a type of fig in Arabic, and suggests that the meaning here is “to scar the unripe sycamore figs (with fingernail or iron tool) in order to promote ripening”, but then translates ובולס שקמים as “picker of sycamore figs”