Unsure of last couple of letters: 6d Spit in Scots isle (parts thereof being exchanged) (4). Does it end in K (as in jerk) or D (as in bit of land)? And I assume 23a begins with M, but why?
Back to the dictionary with 13a, then, Tony - I have "RUSYA", which seemed perfectly sound to me...
Clue for 23a is'Source of millinery, Italian-made - puzzled at this idea?". MILAN seems obvious, but I don't see why.