Fuel cooperative

I have never heard of such a thing as far as pleasure yachts go. Not a coop anyways. Most of your stops will be in Central America and things are well, MUCH different there. Do you know where your stops will be? Or what the routine stops even are? Credit cards do work at all those stops.

Just use a fuel broker:
Gail and Marianne are excellent: tangosierra.us
They will prepay or have the credit necessary to get you fueled up along the way and know all the best agents as needed.

Another thing to be mindful of, as I've done the Atlantic side of this route recently. Not sure how soon you're leaving, BUT many countries have various COVID restrictions and cannot stop there OR need a test within 3 days, which obviously isn't possible if you've been in transit for 3+ days to get there. As of right now Mexico is ok to stop in, Belize NO, Guatamala need a test within 3 days, Colombia NO (although San Andres may be different), Panama test within 48 hours, BUT can take the test when you arrive. I think your best bet as far as logistics go is to fuel in Mexico, and from there straight to Panama.

Most countries won't even let you pull in and fuel or touch land without a covid test within 3 days of arriving. Belize, you cannot touch land for ANYTHING right now, the borders are 100% closed. Right now Roatan is open, but that could change any day now. Talk to Barefoot Cay marina, Gary Lewis is the manager and a really good guy and they should be able to accomodate your size, it's deep enough to get in there. He can also handle your fuel needs, they do tack on $0.20 a gallon over the truck price or the commercial fuel company dock is East of there.

BUT, I have no idea on earth WHAT a commercial fuel broker is going to do for you. You're out of your element when it comes to delivering a yacht. You're not running a commercial ship and taking over 20,000 gallons of fuel. There is only 1 fuel distributor on Roatan, by using a fuel broker yeah you may save $0.20 a gallon, BUT you're going to waste 2 days of your time doing so. Because, who is going to clear you in and out of customs, immigration, etc.? You'll spend 2 days trying to handle clearing in and out on your own, if they'll even let you without giving you some hoop to jump through like needing a Malaria shot, like I saw them do to a sailboater that went to customs on their own. Whereas a marina like barefoot Cay will handle ALL of your customs/immigration paperwork and getting everyone to and from customs for a very nominal fee and you'd be able to clear in/out and fuel all on the same day. Versus wasting the day trying to clear in, then fueling the next day, then wasting a day trying to clear out, while the locals waste your time and make you jump through hoops because they can.
BAREFOOT CAY | Boutique Roatán Resort

Also, not sure why you can't call the commercial fuel supplier directly and get a better price than going through a broker who is going to make a commission on the sale. It's not like Roatan is San Diego harbor with 15 fuel suppliers, it's a small island with 1, so the price is the price. Here's the commercial fuel dock:
Roatan - Clipper Oil

Yes, but Roatan is an entirely different animal. So is most all of Central America......you're not bunkering at sea, you're on a yacht, and well it is what it is. Panama is your only bet of getting a brokered price ahead of time.

In the RV end of it we now have fuel services that pool buyers and negotiate discounts, much like the trucking companies do for their fleets. Substantial at times. I've paid as much as $1 less than the green number on the 100' pole along the interstate. You get a fuel card (proprietary debit card) and you have to be able to take the big nozzle at the truck pumps. It all makes a big difference on a 3000 mile trip.

Be nice if someone would do this for the marine world.

If you can take fuel from a fuel truck, you're getting it about as cheap as you're gonna get it. Off road diesel, no road taxes, only middle man between the port and you is the fuel truck........