Look on Adzuna, Gumtree, Craigslist or any marketplace platforms you might even look on TurnoverBnB. Facebook groups are useful areas where you can find a decent amount of reliable cleaners. When you are vetting a cleaner ask them a lot of questions. Before you meet with potential cleaners make sure you have set your parameters for the type of service and cleaner that you will require. Find where their answers align with your requirements.
Questions to ask:
Do you have STR cleaning experience?
Do you have references from past or current STR clients?
Are you insured?
independent cleaner or part of a cleaning crew?
How do they price? per bedroom/square footage/time?
What supplies do they bring and what do they need from you?
What does an average service include?
i.e. Laundry, deep clean, trash, dusting, etc.