Mo. Rev. Stat. § 115.393

Prior to the primary election, each election authority shall correct any errors or omissions on the sample ballots and cause official ballots to be printed. For each party having a ballot at the primary election, the election authority shall deliver to each polling place a number of ballots equal to at least one and a half times the number of ballots cast in the voting district for the party at the next to last primary election. If no ballots were cast for a party in a voting district at the last primary election, the election authority shall deliver to the polling place a number of ballots estimated to be sufficient for the party.