How to buy $1 U.S. coins?

Could you elaborate on the process of purchasing $1 U.S. coins, specifically in the context of cryptocurrency and finance? I'm curious to understand if there's a direct method or if it involves converting other cryptocurrencies into fiat currency first. Also, what platforms or exchanges are typically used for such transactions? Is there a minimum or maximum amount one can buy? Are there any specific risks or considerations I should be aware of? Your insights would be greatly appreciated.