Missouri Digital Heritage (Secretary of state's website) has an index to naturalization records. I have had some luck finding ancestors in this database.http://www.sos.mo.gov/archives/naturalization/
Play around with alternative spellings to see if you can get a match. I think the 1900, 1910 Census included whether the person was a naturalized citizen and the date of naturalization. (Those dates of course are not always accurate). But it can help you figure out if you have the right person and right time period
You can order a copy of the original record from the Missouri State Archives. However, the information I have obtained on my ancestors from these records has been very, very minimal.