I'm a woman's 12.
Impossible to find shoes. Only one shoe store in our area has a selection of shoes in my size, and their shoes are pretty low quality (but cheap, so perhaps shouldn't complain).
The store is called Payless. No sure where you are, so don't know whether they would be there.
I've also been known to shop at Nordstrom, which does not have a great selection of 12s but has salesfolk who will find them for you and bring them out to try on. They're awfully, pricey, though.
Never had passing issues related to my feet. People don't gender people by their feet. Chest, hair, face, build, walk, voice, but I've never heard of someone gendering someone based on their feet.
I've heard the connective tissue in your feet (and there is a lot of it there) can lose volume as a result of lower androgen levels. Therefore it is possible that your feet could get smaller. Never seen a study, though.