TX excess layer / project-specific umbrella / excess liability insurance

I'm operating an HVAC contractor in the Dallas, TX metro area. My largest customer requires $5M GLI policy, but my agent struggles to place me with a carrier. So far, lots of forms completed with no result. As I understand, regular agents might not be qualified to find the right underwriters for such policies. AI tells me excess layer / project-specific umbrella / excess liability insurance are the quicker paths than the conventional umbrella. Are there any insurance specialists here who dealt with such situations and can advise how to tackle that or recommend a TX agent able to work on such a policy?