Model firm's source of material for programme (6)
I believe the answer is:
sitcom
'programme' is the definition.
(sitcom is a kind of programme)
'model firm's source of material' is the wordplay.
'model' becomes 'sit' ('sit' can be a synonym of 'model'**).
'firm' becomes 'co' (a firm is a company).
'source of' suggests taking the first letters.
The first letter of 'material' is 'm'.
'sit'+'co'+'m'='SITCOM'
'for' is the link.
(Other definitions for sitcom that I've seen before include "'Humorous drama based on situations, in short (6)'" , "Friends, for example" , "Light-hearted TV series" , "Amusing TV series (abbr.)" , "Form of TV comedy" .)