Available as an assembled Module and as a DIY project.
This Module is currently available.
An ADSR Envelope Generator with an AD Loop.
The AI003 Looping ADSR Envelope Generator is a looping ADSR Envelope Generator. It can be manually triggered via Momentary Push Button, Gated via the Gate Signal, Triggered or re-triggered by a Trigger input, or set into a loop mode via a toggle switch. An LED shows the status of the output.
https://aisynthesis.com/product/looping-adsr-envelope-generator-diy-kit/
These merchants probably sell this module. Huh?