I haven't been able to find anything much about the Rifle Brigades that far back.
I would suggest you contact The Imperial War Museum and post all the info you have re his service history and see if they can direct you to where all courts martial info may have come from originally.

https://customerportal.iwm.org.uk/co...311.1545127708

or contact the National Archives re these records:
Registers of courts martial, 1796-1963
And those available on line

https://www.nationalarchives.gov.uk/h...-i-view-online

Fold3 mentioned is part of Ancestry but a separate subscription.