On 2010-09-26, Sam Takoy wrote:

20 cu in is the deepest single gang box available.

You can definitely get them up to 24 in^3, although they will
obviously be bigger in some dimension and so might not fit in your
space. See, for example, www.aifittings.com. But you need 26 in^3
for what you want to do, and I don't know if those exist.

Cheers, Wayne