I sent a side to play in Borneo etc (4,6)
I believe the answer is:
east indies
'borneo etc' is the definition.
'i sent a side to play in' is the wordplay.
'to play' indicates an anagram.
'in' is an insertion indicator.
'sent'+'a'+'side'='sentaside'
'sentaside' is an anagram of 'eastndies'.
'i' going within 'eastndies' is 'EAST INDIES'.
(Other definitions for east indies that I've seen before include "Malay archipelago" , "distant location" .)