you really want this book
http://www.aerostories.org/~aerobiblio/article1845.html
501 Sqn. serials in use 7th July 1940
L: 2038
N:2495
P:2549,2691.2760,2986,3040,3041,3082,3083,3084,334 9,3397,3646,3803
presume you know this site?
http://www.k5083.mistral.co.uk/APS.HTM