Here is a list of some Industrial Hygienists Associations. Check these for reputable Industrial Hygienists to do valid testing for meth and mold. Many companies in the business of doing this testing rely on junk science that is at best a waste of money but may put your health at risk.
Not all Industrial Hygienists are properly trained for the specialties of meth and mold testing. Be sure that the IH you hire has appropriate certifications.
Don't hire an IH who does remediation. A reputable IH will do the testing before and after remediation and design the remediation process for the individual process. He/She will make sure things are done right as an independent monitor.