A supplier of iron, this person blocks trade supply (3,4)
I believe the answer is:
red meat
'a supplier of iron this person blocks trade supply' is the definition.
The definition suggests a singular noun which matches the answer.
'this person blocks trade supply' is the wordplay.
'this person' becomes 'me' (the person writing).
'blocks' is an insertion indicator (upper walls off glass inside formal).
'supply' indicates anagramming the letters (in a supple way).
'trade' with letters rearranged gives 'redat'.
'me' put into 'redat' is 'RED MEAT'.
Can you help me to learn more?
(Other definitions for red meat that I've seen before include "Beef is one" , "beef, say?" , "Beef, lamb or mutton before cooking" , "what carnivores eat?" , "no chicken" .)