I see today Garuda team has updated the Kernel section at the top of the KDE System Settings. 
We now have a LOOOOONG list of what seems to be all TKG available kernels.
Be patient it takes a while to load up and display.
I don't think we can build our own custom TKG kernel from there (sad), but at least it's a lot easier to select up to date TKG kernels and manage them from there instead of from Pamac.
Go take a look and have fun trying out some! 
A list of all available kernels was there for a long time...
Go to Garuda Setting Manager -> Kernels -> Refresh
Never was for me. Even a bit before noon my time it was only showing my installed kernels. Then there was an update of some garuda packages not long after and 15mins later when I went there for another purpose, a long list was showing all available kernels.
Maybe there was a fix of a garuda package and that fix affected my list and I didn't know cuz I always has been affected by the bug? Who knows...
By default, it only shows 1 kernel that is running....
but for all available kernels you have to update....and the refresh button in system setting didn't work...so you have to go garuda setting manager...
I have been using this from almost 2 months for installing kernels