Using do-notation is probably cheating, but what do you think of this? (in Haskell):

  do { w <- widgets;
       s <- sprockets;
       l <- locations;
       guard (l `hasInStock` w);
       guard (l `hasInStock` s);
       guard (w `isUsableWith` s);
       return (w, s, l); }

We're trading horizontal space for vertical space. I think it's much clearer than either list comprehensions or plain map/filters. It's the best of both worlds.