although i wouldn't fit one myself, if you want to try it, here is a link :-
http://www.modelfixings.co.uk/circlips.htm
you can get plenty of internal circlip spares while you're at it for rebuilding the diffs with their (un)user-friendly design of thrust race retention (and yes, i know the design was used in the CAT SX plus i remember them in my Axis TC from years ago - they were crap then too)