Does anyone know where I can buy or otherwise acquire an up-to-date mailing list for rural Custer County? I would prefer something electronic in an .xls format. I can build my own, but I want to do that only as a last resort.

This might help:

http://pe.usps.com/busine...sslist.htm

There are many options; InfoUSA is an option.

You can also mail to "Postal Patron" for rural routes. You need to visit with the USPS office about that.

Custer County has a list however they have not offered to share that public information in the past.

Depending on what your trying to do you might get the sic code of the industry you seek to mail to & buy a list.