Mate supplying porcelain (5)
I believe the answer is:
china
This clue is a double definition.
'mate' is the first definition.
(cockney rhyming slang, mate is china plate)
'porcelain' is the second definition.
(I know that china is a type of porcelain)
'supplying' is the link.
(Other definitions for china that I've seen before include "What's tea" , "It used to be called Cathay" , "Modern name for old Cathay" , "country out east" , "Porcelain ware and country" .)