Yes, indeed difficult to find but I found some in AIR 15. You are probably already aware of these files in AIR 15 which includes combat reports:
- AIR 15/335 Attack/Combat Report Forms, 1939 Nov. 1943 Nov. – 220 Sqn
- AIR 15/371 Air Combats: Records & analysis, 1940 Mar. 1942 Aug.
- AIR 15/650 Air combat reports 1942 Dec - 1944 Nov – Sunderland Sqns
- AIR 15/660 Miscellaneous reports: enemy action and aerial combats, 1940 Apr. 1943 Mar. – RAF Station Mount Batten
I have not checked AIR 15/720 Tactical extracts from combat and other reports, 1941 Jan. 1943 July
I will let you know when I have more info about the combat reports in Canada.