I got lucky to find him yesterday in first and third wave, I found 1 and 3. And I talked to one person who said found him at second wave, and there was 2 of them. So yesterday 6 Cavebears appeared.
I have a friend who spent a long time searching Cavebears to tame, and the number of creatures in second and third waves seems to be really random, depending on your lucky. She told me that at first wave only appears 1 Cavebear, second appears 1-2 and third 2-3. She is a very reliable person, so I can tell that her informations are very accurate.