Based in Poland and selling through Etsy, this vendor has various prison-themed restraints in a few different colours.
I've treated myself to the combined wrist and ankle restraints and they are really well designed and thought out. The velcro fastenings make them adjustable to different size limbs (and they come in different sizes as well) but the tough cotton/canvas material and magnetic locking system mean that they are totally secure once they're locked.
Have a look here:
https://www.etsy.com/shop/StraitJacketShop