If you're looking to gain some kind of qualification there are a couple of online distance learning type courses which include hamsters but don't focus specifically on them. One that was recommended to me was a Diploma in Small Mammal Care by Compass:
https://www.compass-education.co.uk/.../asc-smacc.htm
If you're looking for a more informal way of learning, hamster clubs are often a good place to start. Even if you're not wanting to show, they are a good place to meet other enthusiasts and share ideas.