Amazon has these speaker mounts on hand.
They have a 100 lb capacity. The speaker can rotate freely around the post. There is also an adjustment for degree of tilt. (On-Stage Stands SS-7323B)
I was figuring that these would be a reasonable way to mount speakers on a cinder block wall. I could mount these on either side of the proscenium opening and rotate and tilt the speakers to tune the space. I figure they would also work for other speakers if the current donated speakers aren't adequate for the task.