Awesome, I need pretty much all Moon exclusives:
Sandshrew, Shieldon, Archen, Petilil, Vullaby, Oranguru, Drampa, Lunala, Pheromosa and Celesteela.
Also, Litten and the sea lion.
Any evolutions of these will do as well of course, since I'll breed them either way.
If you want to keep the Lunala, I understand, but just trading back and forth will at least complete my Pokédex. I can trade the ultras beasts for those exclusive to Sun, so it's a win-win, if you didn't haven those already.
Since my ultimate goal is having a living dex, I sorta want to have a Lunala, Type-Null and the extra Cosmog for keeps. I'd trade a shiny Sneasel (shit IV's and nature) and a few 5IV's for it. I've got a decent selection of breeds, in case you're interested.