You can search Staff and Cadet Registers free online. There's a fee of £2.99 to download a PDF image, or you may order a physical photographic print of a particular record.
"The RMA Woolwich Cadet Registers cover the years 1790 to 1793, 1799 to 1805 and 1820 to 1939. Those for the RMC Sandhurst cover 1800 to 1946. Both sets record the name, age, date of entry, commissioning date and corps or regiment joined. Occasionally they can give examination results, information about the father, or in the case of RMA Woolwich, sometimes the school.
The staff registers are more restricted in their time span and what they record. The RMC Staff Register covers 1802 to 1939, the RMC cash books until the early 1950s and the RMA Staff Register covers between 1893 and 1930. However there is often an anomalous entry so it is always worth trying a search."Also available are the RMC Magazine (Royal Military College Magazine), 64 magazines published between 1912 and 1946, and Wish Stream Magazine, 105 magazines published between 1947 and 2011. Access to the magazine collections is via subscription.