Capital that’s unlimited, then hard to come by (6)
I believe the answer is:
harare
'capital' is the definition.
(capital of Zimbabwe)
'that's unlimited then hard to come by' is the wordplay.
'unlimited' means to look at the middle letters (discard the edges or 'limits' of the word).
'then' is a charade indicator (letters next to each other).
'hard to come by' becomes 'rare'.
The central letters of 'that' are 'ha'.
'ha'+'rare'='HARARE'
(Other definitions for harare that I've seen before include "City once called Salisbury" , "capital abroad" , "African capital" , "Zimbabwe's capital" , "City in Zimbabwe" .)