I've seen em on eBay, not there at the moment tho.....
http://search.ebay.co.uk/_W0QQsassZs...isetechQQhtZ-1
is the usuall place, i suspect they are a Kyosho part that aint reached the shops yet - I may be very wrong - but there are also graphite shock towers for the ZX-5 and spares for other cars.
Picture of mount
http://i20.ebayimg.com/02/i/05/d5/50/cb_1.JPG
EDIT: just turned up on eBay:
http://cgi.ebay.co.uk/Alloy-Shock-To...QQcmdZViewItem