A couple of years ago I was also looking for these, but without success. I tried googling, but without a name for them did not have any luck. I tried my usual suppliers - Woodfit, Hafele, Isaac Lord and an excellent local hardware shop (alas now gone). I took a sample in to the Isaac Lord trade counter, but the even the long serving staff there couldn't help. I was able to improvise by using 2 Mini Flush Mounts*, which operate on the same interlocking principle, on each end of the shelf.
If anyone does know of a source would be most grateful.
* Isaac Lord cat no. 219ZP