I don't think there are any LIPOs that can fit that requirement. I looked around while getting batteries for my AK too. I ended up getting this:
http://shop.ehobbyasia.com/bb-batter...y-ak-type.html
But now I see theres one with more MAH:
http://shop.ehobbyasia.com/bb-batter...ry-for-ak.html
Not sure if the 1350MAH one would fit though, the 1200MAH one is already pretty tight.
Both of these are 20C btw.