In plentiful supply (8)
I believe the answer is:
abundant
'in plentiful supply' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for abundant that I've seen before include "Existing in large amounts" , "In plentiful supply" , "Plentiful, ample" , "Exuberant" , "Bountiful" .)