Mo. Rev. Stat. § 115.393: Election authority to deliver official ballots to polls — number of ballots, how determined.

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.