IntroductionMethadone and buprenorphine are effective and safe treatments for opioid use disorder (OUD) and also reduce overdose and all-cause mortality. Identifying and reaching providers of medication for opioid use disorder (MOUD) has proven difficult for prospective patients and researchers. ObjectivesTo assess the accuracy of government-maintained lists of Arizona (AZ) providers prescribing MOUD, and the extent to which these providers are accessible for treatment. MethodsA two-phase study used a listing of 2376 AZ MOUD providers obtained from the U.S. Drug Enforcement Administration and the Substance Abuse and Mental Health Services Administration. Phase 1 assessed the accuracy of the listing using internet confirmatory research from May–October 2022. Phase 2 used the resulting list of 838 providers to assess provider availability, type of MOUD treatment provided, and accepted payment through secret shopper calls between November 16 and 30, 2022. ResultsJust over half (52.2 %, n = 1240) of providers were removed from the original listing during Phase 1. One quarter (25.9 %) were no longer in practice. Among the 833 eligible for the secret shopper Phase 2 study, 36.6 % (n = 307) were reached and identified as providing MOUD. A vast majority (88.1 %) of MOUD providers indicating treatment type were accepting new patients, however methadone was identified far more frequently than was likely permitted or provided for OUD. Providers were 5.5 times more likely to accept new patients if they accepted cash payment for services, and 4.9 times more likely if they accepted Medicaid. Rural areas remained underserved. ConclusionsThe active population of MOUD providers is far smaller than surmised. DEA and SAMHSA provider listings are not sufficiently accurate for survey research sampling. Other means of representative sampling will need to be devised, and trusted lists of providers for prospective patients should be promoted, publicly available, and regularly maintained for accuracy. Providers that offer treatment should assure that public-facing staff have basic information about the practice, the treatment offered, and conditions for taking new patients. Concerted efforts must assure rural access at the most local levels to reduce patient travel burden.