Philosopher one found in short supply (5)
I believe the answer is:
stoic
'philosopher' is the definition.
(type of ancient philosopher)
'one found in short supply' is the wordplay.
'one' becomes 'i' (Roman numeral).
'found in' is an insertion indicator.
'short' means to remove the last letter.
'supply' becomes 'stock' (stock can mean a supply or reserve).
'stock' with its final letter taken off is 'stoc'.
'i' inserted into 'stoc' is 'STOIC'.
(Other definitions for stoic that I've seen before include "he's not complaining" , "One who doesn't complain" , "show little emotion" , "One who endures pain with equanimity" , "Uncomplaining in suffering" .)