You can buy it at a draper's whenever you like (2,4)
I believe the answer is:
at will
'whenever you like' is the definition.
(doing something at will is doing it whenever)
'you can buy it at a draper's' is the wordplay.
I cannot quite see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
'a' is found in the answer.
The remaining letters 'will' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for at will that I've seen before include "Whenever one pleases, own choice" , "take it as I please" , "According to one's own inclination" , "Whenever you please, as you like" , "Freely" .)