If you go on Amazon and search "BDSM locks" stuff like this will pop up. You are probably looking for tiny locks that can be opened with a standard handcuff key.

Hyamass 3pcs Vintage Antique Style Mini Bear Head Archaize Padlocks Key Lock with Keys (Gun Black) https://www.amazon.com/dp/B077JL4KVN/ref=cm_sw_r_apan_glt_fabc_GVPXPWTQ4K1MPA4QKT5M