I had thought possibly to use HCL at one point, but am hesitant to throw it down the drain when it is used. I've used muriatic and probably will do so again, but simply to clean the faces of certain pieces I have done. For commercial rock I want to be able to say that I didn't cut corners or used inferior materials, that to the best of my ability, I used materials known to be safe in the aquarium.
I'll have to check at the local masonry supply - I've never noticed HCL at the big box stores, and online ordering carries a $25US "hazardous materials" charge
Finding it might be the limiting factor...