Are 26C or 28B even real sizes? HELP!

I’ve always had trouble with finding a bra, let alone one that fits. Now a 23 year old woman, I decided to order some bras to try from Aerie (I live in Australia). Because of where I live I was only ever able to purchase 32A which was too large but I had to make do. The Aerie bras that I purchased were 30A. I found the lightly lined ones to work quite nicely but if I lean over there is gaping and you can see inside. The push up bras I purchased did not fit right, they are okay when first put on with the girls squished up but after that it moves and goes weird... Anyway I found this awesome community and used your sizing guide and I AM SHOOK. Apparently I should be wearing a 26C or the sister size 28B. My question is, are these even real sizes??? Where could I possibly purchase these from? Thank you in advance!