Welcome to the Chat to Helplines forum.
I don't know of any wrist support that would be helpful for swimming but a physiotherapist would advise you on this.
Alternating the strokes you do might relieve the pain as it is often repetitive movements that can strain the joints. Changing the position of your wrists by swimming breaststroke, then crawl ( and of course backstroke & butterfly if you're a really good swimmer!) might help.
If you also put this post on to the 'Living with Arthritis' site it will probably get more views and if anyone has any good ideas about how they managed, they will reply to you.