if you're out in the wilderness you can find wheat on grassland and flax on heath (if you can find either of those). look around your area for wild crops for a bit. if you can't find any for a while i'll find a way to get you some in exchange for some blueberries or something.
You can teleport to Brodgar from the adventure menu (travel -> Ring of Brodgar), but if you started with a wilderness spawn it's likely out of your teleportation range.
You can also try to find or trade for hemp instead of flax. It is a source of the same plant fibre that flax is. Hemp is found usually in the marshes that are light greeny-blue on the minimap.