For reference:
The only published official citation would be the announcement in the London Gazette, but this will be a rare example of a case when, for very obvious reasons, it was never gazetted.
There is however a .gov.uk webpage with an excellent secondary cite. The press release from 2002 on the opening of some of the wartime Security Service records provides details of the most notable entries in the diaries of the head of B division, Guy Liddell. One of those entries evidently records that GARBO received his MBE from George VI on 25 November 1944.
http://www.nationalarchives.gov.uk/documents/nov2002.pdf [PDF - relevant entry on p. 44]
YES! That will be an excellent addition to the article! Thank you very much!