It sounds like you have a Corner Creek cage.  I have two of them.  I
bought mine on line at http://cornercreek.com but today the link seems
to be down.
 
I replaced my litter trays with plastic trays from
http://www.craftycreatures.com/forferretsonly/accessories_custom_commode.html
They never rust and are easy to clean.  I've bought 8 trays from them so
far and they have been very nice to deal with.
 
I haven't replaced the flat drop tray yet.  I've been planning to ask
Crafty Creatures how much for a custome built catch tray.
 
John Julian
[Posted in FML issue 4683]