We cannot bundle the ATOM program with SIESTA, as its licensing
options are different.

ATOM is available to academic users at the SIESTA project website at 
http://www.icmab.es/siesta.

For non-academic users, or for those looking for more pseudopotential options, we
recommend a visit to the Virtual Vault for Pseudopotentials:

Use the link http://www.nnin.org/search/node/pseudopotential and
follow the search results.

The best option is to use one of the pseudopotential generators listed
as providing output compatible with Siesta and follow the proper
procedures for testing. Databases of pseudopotentials should be used
with care.