150-days in-game post update and radiant slimes
So after catching 60 radiant slimes in about a 150 days (after the update) I've come to the following conclusions:
2000 slimes to spawn is too big of a pool to look for radiants naturally. I've only gotten two pinks, a single hunter, and a few puddles and fires that way.
There are guides on YouTube showcasing all nine locations on the map, where you can find guaranteed radiant slimes.
Fires are easy to get, if you set a teleport from your base to the Ember Island around the magma pools, you can go to the nearby cave and to the location near my drone that I've pointed on the map. Their pool is only 75 and you can get about 15-20 to spawn when you go there.
Bell rooms don't guarantee radiant slimes, but they have an increased rate of spawning one. Even without decorations. Even if you didn't have one for several days. At some point they will spawn. I've set up teleports to the bell room with a magma pool, the bell room with angler limes, and I've set up a single teleport for the entrance of the area with hyper slimes, because it's in walking distance from two bells and the music room. I've put down a one-way home teleporter near the second bell permanently.
The music room (there's a wall you can open with a nullifier near the exit of the are with hyper slimes, there will be a huge music player room with a bunch of music related decorations) also counts as a room that has a chance of randomly spawning a radiant slime.
Hope that helps!