State of Missouri Code of State Regulations Annotated (Mo. Code Regs. Ann.)
Library of Congress: Mo. Code Regs. Ann.
Mo. Code Regs. Ann. current edition may be held at the Mo. State Library.
In Westlaw, see also historical regulations (coverage varies per state), proposed & adopted regulations - current (covers 2 most recent years & currently proposed and newly adopted regulations), proposed and adopted regulations - all (to search the state's entire register with coverage starting from 2006) and regulation tracking. All links can be found on the state's Regulations page.
State registers and regulation tracking are offered by Lexis, found in its Administrative Codes & Regulations with coverage varying by state. Please note that for some states, Lexis no longer updates the register and offers administrative agency rulemaking activity such as proposal, notice and comment, hearing, emergency and permanent promulgation, and withdrawal only through its Regulation Tracking service. Coverage of the service is generally from 1990 to current.
In Bloomberg Law, proposed, final, emergency, temporary, and interim rules, plus regulatory notices can be found under Rulemaking within the State Laws & Regulation collection.