Welcome back! Like Wolfster said, there are several companions that yield pebbles if you equip them to your wolves. This is probably the easiest ways to make pebbles, apart from doing your current daily activities.
If you're looking for wolves, you can always campaign and hope you befriend a wild wolf, or you can always check the Flea Market for them too. Or breed. Breeding is always fun if you have the space. xD
