You can buy it at a draper’s whenever you like (2,4)
I believe the answer is:
at will
'you can buy it' is the definition.
I can't judge whether this definition defines the answer.
'at a draper's whenever you like' is the wordplay.
I cannot really understand how this works, but
'at' is found in the answer.
The remaining letters 'will' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
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" .)