A loner’s source of Dixieland jazz? (3,7)
I believe the answer is:
new orleans
'source of dixieland jazz?' is the definition.
(New Orleans is famous for its jazz music)
'a loner's' is the wordplay.
I cannot really see how this works, but
'a' could be 'an' and 'an' is found within the answer.
This explanation may well be incorrect...
(Other definitions for new orleans that I've seen before include "US city" , "City of Louisiana" , "port city in the south" , "Devastated city" .)