A razor strop is a leather strip that was used to sharpen straight razors. Often these were used at old time barber shops to continually sharpen the straight razors the barbers used to shave the faces of customers. The need for straight razors and razor strops waned after disposable razor blades became popular.
Shaving with a straight razor typically takes much longer than using disposable or safety razors. And straight razors require a high level of skill and patience - otherwise there will be a bloody mess; straight razors can very easily seriously damage a face.
A razor strop as a punishment implement is serious business, you can really hurt someone, you can easily break the skin; with energetic use you will leave permanent scars.
The Etsy website has several sellers of razor strops, including used and vintage strops. If you really want to buy a strop I suggest an old vintage strop. Remember, these strops can easily hurt someone.
A quick look at Etsy: Search vintage razor strops
https://www.etsy.com/listing/1667441026/vintage-wahl-razor-strops-sold
https://i.etsystatic.com/6921831/r/il/8970a1/6129436205/il_1588xN.6129436205_9rt6.jpg
https://www.etsy.com/listing/1667433718/vintage-razor-strops-sold-separately