Firstly, your question is fine, don't worry. ;)
All Mega Stones are available in Omega Ruby and Alpha Sapphire together, but they can be found in opposite locations depending on the game. The Sharpedoite is found at the Battle Resort in OR and the Aqua Hideout in AS, with the Cameruptite being found in opposite locations. This is the same with Latios and Latias. Latiosite can be found when you receive Latios in OR and Littleroot (from Mum) in AS, with the Latiasite being vice versa.
The locations of all Mega Stones can be found here.
Hope I helped. :)
Source: Above Link