my 5 repetitions are:
48d/41a; 36a/18a; 13d/17a; 19a/7d ; 13d/31d
I don't think that's giving too much away at this point.
jono - ack! I googled 61a and there it is. So there are potentially 5 thematic answers.
This puzzle has taught me more about the theme than I really wanted to know,.