British king, during parade, finds London landmark (6,4)
I believe the answer is:
marble arch
'london landmark' is the definition.
(landmark in London)
'british king during parade' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'king' becomes 'lear' (King Lear).
'during' indicates putting letters inside.
'parade' becomes 'march' (a ceremonial march).
'b'+'lear'='blear'
'blear' placed into 'march' is 'MARBLE ARCH'.
'finds' is the link.
(Other definitions for marble arch that I've seen before include "London monument" , "London sight" , "Capital's landmark" , "national landmark" , "John Nash-designed landmark at northeast corner of Hyde Park" .)