Tarter's gate operation in Dunnville, KY is maybe 30 minutes from me. They are the largest of several gate makers in the south central KY area. You can buy "seconds" directly from them if you make the trip. Or, choose from several other gate makers. Tarter also makes rotory mowers, drag boxes, etc, etc. sold by TSC and others. My place had some white painted Tarter gates in place when I bought it. At ten or eleven years old, they have some rust from a chain banging around where I have some double gates set. Other than that they are okay.
Do a search on "Casey County, KY Gates" for Tarter's website along with a few other makers.
Any powder coated gate or panel is going to rust. I always go with galvanized though they too will eventually show rust at the welds.
The best gate, albeit pricey, I ever used was made by Rohn (think communication and windmill towers, etc. ) who eventually sold off that branch as I recall. I don't even know if they are still available? Anyway, they used a heavier stock which they notched at the cut. Welded up so that the notch was on the bottom, they would hot dip them and the galvanizing would coat inside and out. Working with them, you knew that they were built well because it would take two men and a boy to set one due to the weight, lol!
The only issue was that bees got into the horizontal piping because of that notch. With the usual butt welded pipe gates you only have to worry abouth the vertical pipes.