[Arran]

Ron;
  Any non polarized cap will work, if the voltage rating, and capacitance is right, I've even heard of people using motor capacitors for filters. As you mentioned the main issue is space, even the more modern caps are still more bulky the the equivalent electrolytic, though that four section unit under a 18/118 chassis might be a candidate for it since they are lower value and lower voltage then the filter caps in the power supply, which generally makes them smaller and cheaper, try Mouser's search engine for ideas.
Regards
Arran