Hi Don,
from the index at NARA, I don't recall seeing any entries relating to the night of the 17/18 Aug '43.
Only the British MoD could tell you if a report exists. However, being a relative of the airman concerned, provided that you can obtain written permission from the eldest surviving next-of-kin, you can make a FOI Act request (even from NZ) for information pertaining to your uncle from MoD:
http://www.mod.uk/DefenceInternet/FreedomOfInformation/
If you choose to make a request, be very specific about what you want, namely, copies of: (a) the MRES Investigating Officer's interim and final reports (b) any witness statements pertaining to the crash (c) any German documents relating to the crash.
They will most likely provide you with a written response asking you to complete and return a declaration to be signed by the nok before properly answering your enquiry.
Because of MoD's application of the FOI Act, any information they deem relating to another individual (i.e. another crew member), they will not release without additional nok permissions.
Besides the KE reports (KU reports were for US aircraft), many other documents could have been used by the MRES investigators - cemetery records, police and Stadt records etc.
Another avenue for you is to obtain details from the RCAF casualty file of P/O O A O'Leary RCAF, a member of your uncle's crew. This file will probably only contain info similar to the RNZAF PF file - i.e. correspondence passed on to the RCAF from the MRES via the Air Ministry Casualty branch. The RCAF files are with the Canadian National Archives (and in terms of Canadian privacy laws, if the individual concerned has been deceased for more than 20 years then there is no problem).
Cheers
Rod