Summon Lesser Demons will summon for the caster a number of demons based on a d6 roll; either 2 CR 1 (or less) demons, four CR 1/2 (or less), or eight CR 1/4 (or less).
CR 1 demons include Quasits and Maw Demons; CR 1/4 gives us the Dretch (and Manes are available at CR 1/8). However, I could not find any CR 1/2 demons that the middle result might summon. Searching D&D Beyond for creatures tagged "demon" didn't turn up any demon of CR 1/2.
Does the published material actually include any such demons that this spell result could summon, or is the unlucky caster stuck with getting a measly four Dretches or Manes?