I think these are the original:

https://www.heals.com/blog/icons-masters-chair/

Here are some (at least similar) on Amazon:

https://www.amazon.com/Mod-Made-Century-Modern-Plastic/dp/B01547KLCK/ref=sr_1_12?crid=30HSEOUR8JUFS&keywords=mod%2Bmade%2BPlastic%2BBlack%2BLoop%2BDining%2BSide%2BChair&qid=1654026859&sprefix=mod%2Bmade%2Bplastic%2Bblack%2Bloop%2Bdining%2Bside%2Bchair%2Caps%2C409&sr=8-12&th=1

They're also sold other places though like Home Depot, Wayfair, etc. Prices vary.