The yellow squash blossoms are male flowers where female flowers have a tiny squash attached at the stem. They can be pricey in the supermarkets but I got them for 2 dollars for 30 flowers at farmers markets. Handle the blossoms with care, they can bruise easily. They stay fresh for 3-4 days in the refrigerator.
If you have the space and the time, it’s best to grow your own. My mother used to have a good patch where we could pick enough for a stir fry. We also like them lightly battered and fried (have them with chili fish sauce). Hmmm…yum!