> if anyone knows of any shows needing a newbie steward
Not sure where you're based but if you pick up a few schedules for shows that are near to you, you could phone their secretaries and volunteer your services. If you explain that you're keen but haven't done it before I'm sure they will be delighted to both welcome and train you. Most show societies are often short of stewards.
Also if you look in the events section in the dog papers, there are usually KC approved courses for ring stewards in various different locations. They are also listed in the Kennel Gazette. You can probably track courses down by going on the KC website too.
Best of luck, it's a good thing to do.