If you can't find an extension when using VSCodium then please send a pull-request to this repository https://github.com/open-vsx/publish-extensions with the identifier and that will help grow the ecosystem of open tooling.
ICMYI - We blogged more about this over at:
- https://www.gitpod.io/blog/cloud-ide-history
- https://www.gitpod.io/blog/openvscode-server-launch
- https://www.gitpod.io/blog/open-vsx
If you got any questions lemme know. <3