Has anyone found a site that custom designs swim tops/ braws? If not, what are some solutions?
You might look at the Poland syndrome support group on Facebook...they could probably help.
http://www.spiritoflifeboutique.com/
They sell removable breast prosthetics including ones designed for swimwear. I’m in Australia, am not sure what country you live in but hopefully they will post to wherever (for a fee, ofcourse). All the best & you are not alone :)
..to elaborate ..and they also sell bras & swimwear with bilateral pockets for the removable prosthetics. It is unfortunately expensive :( but of course worth every penny for the confidence.