A chance discovery via Google is that the St. Louis (Mo.) County
Library has online indexes to naturalization petitions and
declarations of intent for the Federal courts in St. Louis >from the
1800s through 1928 or so, searchable by name.

Apparently the St. Louis Genealogical Society has similar name
indexes for the Missouri state courts.

It does not appear that the actual records have been digitized, but
it may be possible to obtain photocopies >from these sources.

For more information:

http://www.slcl.org/branches/hq/sc/nat/nat-project.htm

http://www.stlgs.org/natsearch.aspx

Don Solomon <dsolomon@...>