Can’t find insurance for a field service business

My husband is a diesel mechanic/ heavy equipment technician who has worked for CAT and John Deere. He is trying to start his own field service business, focused on hydraulics lines and wiring harnesses. He has called 15+ independent insurance brokers and carriers for general liability insurance and no one is offering coverage. Has anyone had success getting insurance for this business model?

We are also planning to meet with a business lawyer to see if he could operate with a release of liability and the LLC.

Any insight is appreciated.