I would have expected the owner/operator of G-DAZY to have lept in to ensure that the headset was either found or replaced. They after all were the ones that were greatly assisted by your deed and they should therefore find/replace the missing headset forthwith together with an ex-gratia payment as a gesture of goodwill!
This is an absolutely disgraceful situation.
The aircraft appears to be currently owned by:
CENTRELINE AIR CHARTER LTD
C/O BRISTOL FLYING CENTRE
BRISTOL INTERNATIONAL AIRPORT
BRISTOL
BS48 3DP
UNITED KINGDOM
I am guessing that they were the owner/operators at the time of your loss, lets hope that their conscience is prodded by this thread!