I have a thing where I save the game before I buy items from the battle maison in Kiloude city. So I can test the items on my Pokemon in online battles (I have the 'don't save' option set when I do online battles), and if the items weren't that good, then no problem, I can just quit and go back to where I saved. This is great because it saves battle points and you don't lose any friends/aquaintences and their friend codes if you go back to when you saved.
My search for Diggersby may be in luck, because the 51st friend I recently added had the ground Safari, AND had 3 Pokemon in it, which means it may have Diggersby in the last slot. The new item I bought for my Avalugg was the red card, and wasn't very good sadly, but I didn't want to waste 32 BP, so I quit and went back to where I saved.
To my horror, my friend wasn't online anymore, and the ground safari only had 2 POKEMON in it (dramatic music). When I saw this I was like NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOIfYouGotThisFarThenCongratsHaveAFreeCookie.
So I'm PRAYING that someone knows a way to get the third slot available (aside from waiting for my friend to be online)