UPDATE

I've been in contact with the store and I have narrowed down the date and time that the cards were lost. They don't have details about the names of who was in store at the time since we weren't playing during an event. I will be putting up some more detailed posts in my local area and that will hopefully help. If the owner doesn't approach me in the coming week or so I will try and organise a sit down with the store owner to look at the CCTV footage and find the face of the owner.

So abit of context, a few weeks ago I was playing commander at a LGS nearby. I was playing my colourless eldrazi deck. I cast [[Oblivion Sower]] and exiled four cards off of my opponents deck. Two of those cards happened to be [[Cavern of Souls]] and [[Polluted Delta]]. Naturally, I put them into play and continued playing.

The problem is, the sleeves that my opponent were using were almost the exact same colour as the sleeves I was using, so by the end of the game those two lands just blended right into my board and I forgot they weren't mine. I must have just shuffled them into my deckbox because I've just noticed them in there today.

I'm not sure what to do? I'm not comfortable enough with this store to give them the cards and trust they will find the rightful owner. I also can't remember the opponents name or the exact deck they were using. I think I remember what they look like, but I also played with a number of different people so I'm not 100% confident. I'm contemplating putting some posts up on local mtg Facebook pages but he may not even know the cards are missing. I wouldn't notice if two random cards went missing out of one of my decks? I plan to go back to the store on a weekly/bi-weekly basis, should I just keep an eye out for someone who looks familiar?

If the cards weren't so expensive I probably wouldn't be as stressed out, but these 2 cards are more expensive than some decks I own.