I believe that you should be able to find the Arkenstone in The Lonely Mountain.
It will be like Gollum where there is only one and if it is lost or destroyed you cannot find another one. If you have the stone in hand when you walk around Erebor, Dwarfs will cheer for you. The Arkenstone can also be put in Dwarven brick and will make the Block glow.
Thank you for reading and I hope that you would consider putting the Arkenstone in the renewed version of the Mod.