I buy gas for my three cars that take premium at Costco every chance I get. I have never had a problem. I did have a problem at BP years ago when their gas was contaminated. If no Costco around then I buy it at Sunoco. No more BP for me.
Where I live we can still buy ethanol free gas . I gladly pay a little more.
You're lucky that you can find those stations. I read somewhere that the major refineries deliver ethanol-free fuel to the terminals. The ethanol is delivered by truck and rail to the terminal and mixed locally. YMMV