Hypoallergenic or Nickel-Free Padlocks and Keys for Sensitive Skin

Has anyone managed to find hypoallergenic chastity devices? Particularly those that are nickel-free… My wife wants to wear the key on a chain around her neck, but she has sensitive skin when it comes to jewelry (rashes, inflammation, allergic reactions or intolerance issues). It’s not too hard to find suitable chains for her neck, but finding the right padlock—or more accurately, the correct key—is trickier. I don’t think she plans to wear a full-sized padlock around her neck. Has anyone else dealt with this dilemma? Thanks ‘Yeldarb’