glenmore, they are LARIN brand, I bought them at Menard's (a big Midwest home-improvement chain). They are a cheap Chinese import, under $20 for the pair if I remember correctly.
It was the last box they had available in several stores I checked... it appeared Menard's was replacing them with the more common ratchet adjustment, which I don't trust, especially on a cheapo stand. I like the through-pin design where I can readily see the pin is engaged.
Other than that, they aren't the greatest... the post wiggles around a bit inside the support tube, and the four legs aren't exactly the same length. I haven't ground down the oversize legs because of the above-mentioned fear... I don't know if the heat would cause the metal to weaken. Is there a metallurgist in the house??