The Amstrad User Mail Order Service
I used to personally order software from their Mail Order Service in the late 80s and early 90s which was really good in terms of what you could get. I do recall though that you could indeed order Tapes or Discs from the programs listed in their magazine through their Mail Order Service (though their subscription service did entitle someone for a tape with the magazine). The deal with the Discs though only came with the Mail Order Service I think and it would consist of programs over a number of issues of TAU.