Goodbye note found on floor in Japan (6)
I believe the answer is:
tatami
'found on floor in japan' is the definition.
(japanese floor mat)
'goodbye note' is the wordplay.
'goodbye' becomes 'tata' (I've seen this before).
'note' becomes 'mi' (as in 'do re mi').
'tata'+'mi'='TATAMI'
(Other definitions for tatami that I've seen before include "Jap. floor mat" , "Japanese straw mat; a mat, it (anag.)" , "Japanese rush and straw matting" , "Floor-covering" , "Jap. room matting" .)