The DH114 was certified by the UK in 1950 in accordance with Airworthiness Approval Note (AAN) 01447 and the CAA may not have issued a type certificate and data sheet at this time. You can search the AAN database for DH114 on the link below. You will probably need to ask the CAA for a copy of the AAN or any other AANs you require.
Airworthiness approval notes (AANs) | Civil Aviation Authority (caa.co.uk)