Lost remote for model 4640X how do I get replacement

You buy a new one at Walmart like the rest of us. That model is way out of warranty period. 

The 4640 will work with any Roku remote you can buy anywhere. It can use the simple Basic Remote (IR only) or any of the Voice Remotes (WiFi Direct). Since it can use an IR remote, you can even find very inexpensive universal IR remotes (less than $10) and almost any store that sells remotes. Just make certain the packaging lists Roku players as a supported device. 

Hi, Poolfrog

Thanks for posting, and welcome to the Roku Community.

The Roku Ultra model 4640X is compatible with the Roku Streaming Players remote and the Roku Voice Remote. These two are great options for replacing your lost remote.

For more information, you can check the links below:

Roku Players Remote

Roku Voice Remote

We hope this helps, and let us know if you need further assistance.

Best,

The Roku Community Team.