You might try soup or tuna cans. Check out this link...
http://www.cakecentral.com/cake-decorating-ftopict-10273-soup.html
I have a 2x2 3x3 and a 4x3 I got off ebay and they are labeled magic line pans, I got them off ebay but since they're magic line I would do a serch on magic line pans to find them. Also I have seen silicon pans that have several cavities like 6 maybe that make very small square cakes like 2 and 3 inches. Just not sure where I saw those.
I just made some mini cakes and instead of trying to find the pans I just made a cake in one of my square pans (I needed a 3" circles and i used a 6" square) and used my 3" circle cookie cutter to cut out the cakes. it was perfect and my waste was very minimal. I will say the batter I use makes very dense cakes that are ideal for carving. I would think that this may not work as well it your cake is fluffier, crumbly, or does not bake flat on top (would cause your cake to be sloped on top).
i hope this helps a little.
Heres another one.
http://www.fancyflours.com/cake-pan-round-2-2-deep.html
Also maybe you could bake a square cake and use a deep round cutter to get the size you want.
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