There's an easy way to find it. Use /dt (Pokemon), gen 7. If it shows "Error: No moves data found for in [Gen 7].", that means that Pokemon isn't available in Random battles.
So the ones are:
Cosmog, Cosmoem
Error: No moves data found for Cosmog in [Gen 7].
Error: No moves data found for Cosmoem in [Gen 7].
Keldeo-Resolute
Error: No moves data found for Keldeo-Resolute in [Gen 7].
Mega Rayquaza
Error: No moves data found for Rayquaza-Mega in [Gen 7].
Meltan
Error: No moves data found for Meltan in [Gen 7].
Source: /randbats [Pokemon], gen 7
It's interesting to know that Phione is no more available in Gen 8, but it was in Gen 7.
Hope this helps!
