At The National Archives in Kew. ORBs for OTUs have not yet been digitised, so you would need to visit.
Reference is AIR29/669 and the description says: '26 Operational Training Unit (OTU). Formed at Wing (UK) in November 1941. Contains a copy of the handbook 'So This Is Wing' (an introduction to the station's surroundings and facilities) and two editions of 'Target' (a review of current affairs and topics). Includes photographs of a military parade at Wing, an arts and crafts exhibition and interior views of the Intelligence Library. With appendices.'
It covers the period November 1941 - April 1946, which seems at odds with the date you have mentioned.