Color spray and sound burst are the only ones I find below 6th level after a quick glance through the SRD. Plenty of monsters have stun abilities, though, I think. Edit: so it's odd that there aren't more spells.
Do any other constructs have stunning attacks? Maybe we can look at their construction.
Dmg 1-6/1-6 (Fists)
SA +1 on initiative rolls, spell use, drumming
SD spell use, immune to mind-affecting spells, poisons, paralysis, and gas attacks; saves as 16th-level magic-user; 15% magic resistance
This infuriating creature was once a ventriloquist's dummy, but by some hideous arcane means it took possession of its owner's mind and now possesses his intelligence. Qhyjanoth has given it greater powers by magical means, and in exchange it is serving him for a limited duration. The puppet can cast a ventriloquism spell six times per day (with which it causes maximum distraction and confusion) and the following spells once per day each: command, hypnotism, improved invisibility, and suggestion. The puppet may use only one of thes spells per round. It is armed with two rods of wood and metal with which it can beat out a tattoo on any solid surface. After three continuous rounds of listening to this drumming, PCs must save vs. spells or be confused as per the duration of the drumming and for 2-5 rounds after it stops. The puppet can melee and use spells in the same round, but while drumming it cannot undertake any other offensive action or cast spells. It attacks anyone but Qhyjanoth--but, unlike the zombies, it will flee after Qhyjanoth if it is injured.
Drumming (Su): As a full-round action, a ventriloquist puppet can beat a rhythm on any solid surface. After three consecutive rounds of drumming, any creature that can hear the drumming must succeed on a DC X Will save or be confused (as the spell) for as long as the puppet continues to drum and for 1d4+1 rounds thereafter. The save DC is Charisma-based.
Spell-Like Abilities: 6/day--ventriloquism (DC X); 1/day--command (DC X), greater invisibility, hypnotism (DC X), suggestion (DC X). Caster level Xth. The save DCs are Charisma-based.