Lists of thatchers can be found at:
Each organisation has technical standards to which members must meet. Some thatchers also advertise independently.
A local thatcher should be familiar with the regional vernacular style and materials.
It is useful to find out and visit other projects a thatcher has carried out and speak to clients and local authorities who have worked with them.
The thatcher should inspect the property and discuss with you the repairs needed. They should provide you with a written quotation, itemising the works and materials.