I know that Newegg, TigerDirect and Amazon sell them. Usually the rackmount systems are aimed at being used as servers.
The question You need to think about beyond the CPU, memory would be Do You need to put PCI or PCI Express cards into the case. You will find that the size case You indicate, which sounds like a 2U will have limited Expansion card and possibly drive space.
One Other Drawback is that if the power supply goes bad You will not be able to run to a computer store for a replacement.
And You will be paying a premium for a rackmount computer compared to a Desktop computer for the same specifications.
P.S. You usually find a rackmount unit to be noisier. In My experience the 1U servers I assembled for others all sounded like a Jet engine when powered on and got quieter after the P.O.S.T. quieting down to a almost Tolerable noise level. That is because in a 1U or 2U the fans are smaller so they run faster creating more noise.
Edited by rotor123, 08 December 2013 - 10:42 AM.