The following companies provide Munki training, a managed Munki solution, professional support for your own Munki deployment, or some combination of the above.
(These are not recommendations or endorsements, but merely a starting point for your research):

Australia:

• Automatica Pty Ltd
• eWhizz

Canada:

• iAdvance IT (Ontario)
• Clicpomme (Québec)

Czech Republic

• Etnetera Logicworks, s.r.o. (Prague)

Finland:

• mcare pro Oy

France:

• Amaris
• Abelionni

Germany:

• AgenturAdmin
• Creative IT Service GmbH
• wycomco
• Zentral Pro Services GmbH

Netherlands:

• UPTIC.IO

New Zealand:

• Imagetext Integrated Solutions

Sweden:

• Dicom Data (Stockholm)

UK:

• Gal

USA:

• Helix Systems
• The Linde Group
• Mac-MSP
• MacTechs
• Technology Revealed, LLC.
• Technolutionary
• Third Vantage
• Valiant Technology
• VirtuaComputers

Russia:

• Forward Media Group

Spain:

• @LcTrKiD

Switzerland:

• Amaris

Worldwide:

• Amaris
• Abelionni
• Centrify
  Centrify is a vendor of management products for Mac, Windows, and Linux. Centrify offers and supports "Application Management Powered by Munki". This is a commercially-supported Munki implementation. See this announcement for more info.
• SimpleMDM is a client management tool that bundles Munki for software management: https://simplemdm.com/features/munki/
• VMware Workspace ONE
  Workspace ONE is set of cross-platform client management tools. Workspace ONE's Mac software management is powered by Munki: https://docs.vmware.com/en/VMware-Workspace-ONE-UEM/services/Software_Distribution/GUID-AWT-HOWMUNKIDECIDE.html
• Zentral is a client management suite that bundles Munki, Osquery, Santa and MDM for managing endpoints. Source available and supplemented by stellar Enterprise Support.