The usual solution is to use an external off the shelf power supply module, makes all the mains safety certification pain go away.
I would be very reluctant to bother designing my own off line switcher for a product, especially for something jellybean like a micro plus peripherals sort of thing, the costs of certifying it for every interesting market would be such that just buying an off the shelf line lump is highly attractive (And if 5V @ 500mA will do you then, USB?).
Even if I was designing something that needed an internal power supply, I would still be thinking in terms of a brought in module, Meanwell IRM series or whatever, problem solved, onto more interesting things...
If you really wanted to do your own flyback for some reason then Coilcraft, Wurth and others have transformers for specific chipsets, but it is seldom worth the pain.
Regards, Dan.