Where is a new repository for groovy?

[goinglinux]

Welcome @Ansley, to the Ubuntu-MATE Community!
You can download the latest iso files for Raspberry PI including PI 4 here:

Choose a release | Download

You can find more information about the releases for the Pi here:

Raspberry Pi | Ubuntu MATE

Also, here is a community post on a successful upgrade that you might find useful:

Raspberry: do-release-upgrade to 18.04 LTS

Dear all. I’ve recognizd that the new version (at least of the origin version) 18.04 lts of Ubuntu mate is avaiblable. Because I’ve learned that it is no good idea to try to upgrade the Raspberry version of Ubuntu mate directly by do-release-upgrade I’ve investigated how to perform the upgrade safely. As I have found out it seems the only way of safely upgrading is to install the new version completely new. Because the version 16 is running smoothly now I don’t want to hazard this installation …