Mo. Rev. Stat. § 473.057
If a witness to any will for good cause shown is prevented from attending at the time when any will is produced for probate, the clerk or court may issue a commission annexed to the will or a photostatic copy thereof, and directed, if the witness resides out of the United States to any court having a seal, of any state, kingdom, republic or empire, or mayor or other chief officer of any city or town having a seal, or to any minister or consul of the United States to any country in which the witness resides; if without this state and within the United States, to any court having a seal, or to any notary public in the state, territory or district in which the witness resides; and if within this state, to any court having a seal, or judge thereof, notary public, mayor, or other chief officer of any city or town in the county where the witness resides, empowering him to take and certify the attestation of the witness. If any witness is a member of the Armed Forces of the United States on active duty and out of this state, the commission may be issued to any commissioned officer, other than a warrant officer, of any of the Armed Forces of the United States, on active duty, and shall authorize him to take and certify the attestation of the witness.
§ 473.057, RSMo
Effective 1/2/1979