Sorry to hear the brokers you are working with aren't open to creative financing. In my world it's pretty standard. As a broker, I do have the conversation very early that in order for me to go to work, the commission has to come from somewhere. Usually, addressing where the commission will come from can be worked out with relative ease however.
90% seller financing would allow a buyer to put down 10%, giving the seller some cash to pay towards closing costs, broker fees, etc. If the plan is 100% seller financing, then your broker would have to either secure their commission from you or the seller outside of that. If neither are willing to do so, it can become a very unfruitful for the broker.
I would just make sure to have the conversation early on that you are an experienced investor who has closed "x" number of deals in the area and a major strategy you implement is seller financing. Let the broker know that you fully intend on helping them get paid either from you or the seller, if they in turn help you secure great deals.
If you can't find a good broker in your area to help, you could contact an attorney to draft the offer for you and present it to the listing agent yourself. They would have an obligation to present that offer to the seller.