When trying to catch one of these, if you don't see any start killing the Infested Bears. When they respawn they have a chance of being "momma bears." That is, they'll have a cub following them. If you're hunting for a rare quality cub keep the momma bears alive, the cubs will keep respawning next to that bear.
Also, it doesn't show in the pet journal but the bear cubs have spider eggs growing on their back just like the Infested Bears.