True, there may be several reasonable answers for the clue for 21 ("Maybe you can find them
") and I won't be surprised or upset if someone points us towards a better answer.
In the meantime, the "focus" answer seems to me to work as it is quite well known amongst fans. And ... I can just imagine the clue-setter sitting there taunting us just a little with his/her original clue.
On the same note and to a greater degree, I bet there are several perfectly reasonable answers to clue no. 14 ("Travelling salesman must think this
"). The 'correct' answer is anyone's guess, really.