The trick is to use the _all_docs and then select the ones that you are interested in out of that list with the startkey and endkey.
Since all design documents _id starts with _design/ we can select all docs between _design/ and the following character which is 0, giving _design0.
http://www.couch.db:5984/database/_all_docs?startkey="_design/"&endkey="_design0"
Best of luck!