Ubuntu MATE 19.04 live ISO available: http://cdimage.ubuntu.com/ubuntu-mate/daily-live/current
This ISO gets refreshed daily and 19.04 is currently in alpha testing stage, so I wouldn’t recommend installing on real hardware! A virtual machine is the way to go if you want to test ISOs for unreleased versions of Ubuntu. You can use VirtualBox, VMWare, or QEMU/KVM.