We have 16 concrete blocks, free to anyone who wants them.  Some of the smaller ones have a bit of mortar  clinging, but not much.  Take one, two...all, whatever you need.

Here are the dimensions:
   --five of them are 7 1/2" w X 11 1/2" h X 15 1/2" l
   --eight of them are 7 5/8" w X 7 5/8 " h X 16" l
   --two of them are 7 1/2" w X 7 1/2" h X 15 1/2" l
   --one is 7 1/2" w X 11 1/2" h X 16" l

We're in Highland Park on Stanton Avenue.  If by chance you want a photo of the blocks, I'll be happy to send it.