Is there any external CD drive for iMac 27"?

The Apple USB SuperDrive is no longer listed in the Apple online store, and was IMHO not the best option available for modern Macs. It was last updated 12 years ago and was only USB-2. It was bus powered, meaning it had to scab all power from the computer's USB ports.

My drive preference for a desktop computer is a self-powered optical drive using a tray-loading mechanism. They are the most reliable. We are now the verge of ordering a new iMac for my wife, and she needs an optical drive. This is the one she will get:

https://eshop.macsales.com/item/OWC/MR3USD24

It is a tray-loader with an independent power supply, and is USB-3 rated. Its power and data cables are separately replaceable if damaged, unlike the SuperDrive's permanently-mounted cables. If the cat chews up the combined power/data cable on an SuperDrive, you get to buy a new SuperDrive. 🐱

All

There are many Mac compatible CD drives such as the Apple SuperDrive, those that macsales.com and amazon.com have available.

Pretty much any USB CD/DVD drive out there can be used with a Mac.

What specifically are you looking for?