Shop for some assorted posters (5)
I believe the answer is:
store
'shop' is the definition.
('store' can be a synonym of 'shop')
'for some assorted posters' is the wordplay.
I cannot really see how this works, but
'for' could be 'to' (eg both can mean 'in the opinion of') and 'to' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for store that I've seen before include "Put away for future use" , "Save" , "Put by; shop" , "Supermarket" , "Shop; repository" .)