There was a site that could beat the AI every time for the Innkeeper (a gloating expert in AC3). I'll try to see what that was I think it might have been the merrelles site, which required my gaming PC to run (would not work on my laptop).
As for the 'cheevo, I'd try Fanorona. That's what I used. The game is actually pretty interesting (okay, nerd alert - I've also been a chess geek since an early age, so maybe it's just me), and not difficult to beat on Intermediate. You can make several mistakes and still prevail. 500R per win (on intermediate) is far nicer than 100, and I'm betting you're all at stages where several thousand R are pretty much meaningless.
For Fanorona, try an "open" opening, by moving the piece that can move diagonally from your L to R. Go from there. Usually, you can move carefully, keep your R side (opponents' left) basically frozen while destroying your enemy's R side. Protect your corner and don't get greedy so that the opponent can chain a giant destructo-turn against you, and you can then crush him.
The Fanorona AI is particularly bad in open games in the mid-game, IMHO.
1) Download the Windows version. 2) Go to Options, Configure AI, and set Computer B's thinking processes to 'max. time 15' and 'max. depth to 50' 3) In Assassin's Creed III, do not go first and put your bet to £100. 4) Now for every move that the AI makes in Assassin's Creed III you will be making in the morris.exe. 5) Every move the AI in morris.exe makes you will be making in Assassin's Creed III. 6) ??????????? 7) SUCCESS!