Sudden emergence of available supply (7)
I believe the answer is:
outcrop
'sudden emergence' is the definition.
(I've seen this before)
'available supply' is the wordplay.
'available' becomes 'out' (I've seen this in another clue).
'supply' becomes 'crop' (I've seen this before).
'out'+'crop'='OUTCROP'
'of' is the link.
(Other definitions for outcrop that I've seen before include "Exposed rock formation" , "Not suitable" , "Poor cut (anag.)" , "Rocky feature" , "Part of a rock formation above the surface" .)