The professional wedding and portrait photographers that I've known have generally been members of Professional Photographers of America (PPA). If you're not a member, you may want to consider joining in order to network with other professionals in your local area. To my delight, it has been my experience that professional photographers tend to be
both competitive
and cooperative with each other and willing to share knowledge and advice.
I am aware that some of them had business insurance thru the PPA association. Whether it's a good deal or not I couldn't say, but it's a place to start for comparison.
https://www.ppa.com/benefits/insurance