It’s not often there are new models (6)
I believe the answer is:
seldom
'it's not often' is the definition.
('seldom' is the opposite to 'often')
'new models' is the wordplay.
'new' indicates anagramming the letters.
'models' is an anagram of 'SELDOM'.
'there are' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for seldom that I've seen before include "Alluvium" , "Not very often, rarely" , "Not often, infrequently" , "Not 21" , "Only occasionally" .)