Help me find a wall safe that is 10”L 10”H and 4” deep ?

There are plenty of safes of that general size.  You cut the wall to fit the box.  Which brings up a point.  Any burglar knows to tear through walls, etc to get what he wants.  Your safe is not safe because he can carry it off with about 30 seconds of effort.  You would be much better off hiding whatever you have by concealing them.  Spend some time and effort in concealment as opposed to an obvious safe.  For example, your stuff would be safer if stuck in a fake electrical outlet behind a sofa because it looks like all of the other outlets.  

They are generally sized by how many bricks came out to make the hole. 

You are looking for a 3 brick safe as the nearest size.