Mega Evolutions whose Mega Stones and their species are attainable in Moon, without transfer:
- Mega Alakazam
- Mega Slowbro
- Mega Gengar
- Mega Kangaskhan
- Mega Pinsir
- Mega Gyarados
- Mega Scyther
- Mega Sableye
- Mega Sharpedo
- Mega Absol
- Mega Glalie
- Mega Salamence
- Mega Metagross
- Mega Garchomp
Mega Evolutions whose stones are available in-game but the species are unavailable natively (will be available via transfer in January 2017):
- Mega Venusaur
- Mega Charizard X
- Mega Charizard Y
- Mega Blastoise
- Mega Rayquaza
- Primal Groudon
- Primal Kyogre
Other Mega Evolutions are unavailable as their stones are not natively attainable in Alola. However, it's most likely that these stones will be attainable in further Gen VII instalments and can be traded into Moon to achieve Mega Evolution.
Hope I helped. :)
Source: http://www.serebii.net/sunmoon/megaevolutions.shtml and my bloody fantastic mind
