Size 9 is actually the most common shoe size in women, that’s why you can’t find your size at thrift stores. TJ Maxx and Marshall’s are the same for me. Never any 9’s, but tons of smaller sizes.
8.5 is the average foot size of women in the US and when you consider that the average height is 5'4, I think you're just fine. You're just a half size up for the average.
I'm 5'10 with a size 10 foot. I was a 9.5 for years and then I became a 10 after having a baby....then I had my 2nd and now I'm a 10 and all my newish size 10 shoes feel snug😭. I dont know if I'm quite a 10.5