In my state you can only trade face to face with another officer. There is no regulation about trading patches but it is not allowed to wear a patch if you aren't a LEO. Impersonating a police officer is a crime here and there.
And to the OP, if you want to trade a patch or two, LMK. I collect since 1989 and have a bunch in my trade stock.
Evenhand (Cop Movie): You can't be everybody's friend
There are two things I'm good in, the second is arresting people
I'm looking for Drug/Narcotic Unit patches together with DUI/DWI unit patches for a frame in our Anti-Drug-Team bureau
Also looking for Massachusetts Police and US Capitol City PD patches now!