I have my gear covered as a rider on my homeowner's policy.
Maybe you need a new agent/broker or a new insurance company? I've done this for many years with two different insurance companies, and I've had no issues with either company. The first was State Farm who we had since living in CA, but they have no agents in MA and stopped writing new policies here long ago. I dealt with their 'policy service office' to drop gear that I sold and add gear that I bought each year. We switched when we moved to a new house in the same town 9 years ago, and we're now with a different insurance company through a local insurance broker.
I'm sure you'd need to show your proof of purchases, regardless. I did when we switched insurers, and when I buy new gear I just send my insurance broker a pdf of the invoice (usually from B&H) and they add it to the policy (likewise, when I offload gear I just email them and they remove it).
I pay 1.3% of the value of the covered gear for full replacement coverage, worldwide including theft/loss. I don't put the small stuff on the policy, only gear costing >$1K is on the schedule, but the total is well north of $50K. My broker didn't bat an eye at that when we opened the policy, she just said send me a list and the receipts.
Gear coverage on a homeowner's policy is only possible if you don't make money with the gear. If you do, you need to look for 'inland marine' coverage. I suspect you're going to pay a substantially higher rate for that type of standalone coverage.
