The only engine maintenance course I know of is for diesel engines and it's an RYA course. You could try checking any local colleges.
Otherwise, 'Digital Vision' (who have produced 3 good RIB videos: RIB Cruising, Extreme RIBs & Small Boats, Big Seas) have also produced a video 'Outboard Troubleshooting'. It costs £19.95 and the blurb says:
"Presented by Andy Clark, this video covers the subject of how to troubleshoot 2 and 4 stroke outboard engines. Aimed at those with little mechanical knowledge but with an interest in taking a more active part in the upkeep of their outboard engines. It demonstrates how to carry out basic DIY maintenance, servicing and winterising, and could save you a lot of money in servicing and repair bills. Also included are the most common causes of breakdowns at sea, how to avoid them, and what emergency items to take with you in the event of breakdown."
I haven't seen the video but sounds like it could be what you're looking for? (Although not as good as hands on learning in a workshop, I guess!)