Orders in Council are made by the Queen acting on the advice of the Privy Council and are approved in person by the monarch.
Orders “in” and “of” Council are no different from other forms of delegated legislation. Where they are statutory they will usually involve a Parliamentary procedure. Where they are prerogative they will usually be of no particular public interest, other than to the bodies to which they refer.
Orders in Council are published from 1665 in the London Gazette, which contains a subject index from 1848, available online at the Gazette website https://www.thegazette.co.uk/
The Gazette enquiry service are very happy to help with enquiries: https://www.thegazette.co.uk/researchservice