Yes, I have encountered challenges like this in your testing sector, due to the nature of your test measurements and the sampling criteria.
In the event that no formal PT scheme is available for testing and sampling, the the laboratory must propose a suitable alternative that is agreed to by the accreditation body. The policy document ILAC-P9:06/2014 ILAC Policy for Participation in Proficiency Testing Activities is applicable to this situation. It is available at https://ilac.org/publications-and-resources/ilac-policy-series/
My recommendation is to contact the Accreditation bodies that you may select to be assessed and accredited through. Many have accreditation programs (added to ISO 17025) for specific sectors. This is driven typically due to national legislation related to air emissions and engagement with regulatory bodies and associations. This means the accreditation body will have policies and requirements to accommodate such laboratories. These can be in addition to the ISO 17025 requirements, or a risk-based approach to implementing ISO 17025 requirement.
Then also seek out information from regulatory and other laboratories in your sector regarding standardisation group /subcommittees and associations in your region to establish what the sector solutions are