how to i find the key url for ubuntu hirsute

I know that is the one for bionic "http://keyserver.ubuntu.com/pks/lookup?op=get&search=0x3b4fe6acc0b21f32"
I looked at https://keyserver.ubuntu.com/pks/lookup?search=hirsute&fingerprint=on&op=index and got nonthing.
How do i find the one for hirsute.