I found the following Walrus flights mentioned in the war diaries of the US warships that participated in convoy PQ-17:
HMS NORFOLK catapulted one plane at 2134 on 2 July 1942, recovered 0010 on 3 July
HMS LONDON catapulted one plane at 1624 on 3 July, recovered 1818
HMS LONDON catapulted one plane at 2130 on 3 July, recovered 1247 on 4 July - towed back to the cruiser by HMS LORD MIDDLETON
HMS NORFOLK catapulted one plane at 2137 on 3 July, recovered 2336
HMS NORFOLK catapulted one plane for ice reconnaissance on 4 July, did not return
I also found the following note in one of the war diaries: "HMS LONDON is reported to have had a plane damaged by a Snooper and NORFOLK to have lost a plane on this trip, possibly from Snooper stalking."
The details are probably mentioned in the ship logs of the British cruisers, available at the National Archives:
ADM 53/116173: Ship log HMS LONDON for July 1942
ADM 53/116387: Ship log HMS NORFOLK for July 1942