Regularly sourced raw material (3)
I believe the answer is:
ore
'raw material' is the definition.
'regularly sourced' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'sourced' are 'ORE'.
(Other definitions for ore that I've seen before include "14 [CURRENCY UNIT]" , "Small coins" , "coinage" , "Raw metal" , "15 down earth" .)