There are 5 Russian consulates and each of them services specific US states – you can find which consulate services your state in here: http://www.russianembassy.org/page/russian-consulates-in-the-u-s
For example, if you are from Missouri, you need to apply to the Russian consulate in Houston. Here's their page: http://www.rusconhouston.mid.ru/eng_main.htm
Since 2012 Russian consulates do not accept visa applications directly, it has to be done through their affiliate visa processing company, ILS. This visa processing company only accepts documents on the walk-in basis or through a personal appointment. You can contact them to see if they will accept your documents by post – please, tell us what they tell you, so we can inform other travelers. Here's their website (for the ILS visa application center in Houston) – http://www.ils-usa.com/main.php?id=contact4&lang=en
If they don't accept documents by post, you can use a local US travel agency - you can find a recommended one on here: http://www.waytorussia.net/RussianVisa/Agencies.html
(they'll charge extra though, so it may even be cheaper for you to actually travel to Houston to apply in person).
To get visa support documents, use http://waytorussia.net/Travel/VisaSupport.html