I guess my RNG must really be terrible then, have now gone over 100 days in Dream World (on 70 luck) without seeing a single one, don't see anywhere new to go or any new dialogue box. L hasn't given me any either (though I did get the final Dwarven Cogwheel I needed for a clothing set so there is that).
Not seeing anything in the Library that helps per se with this specific thing, but I may not be looking in the right place. Thank you for the response though, much appreciated!
Will try maxing out Selena's relationship to see if that makes any difference on the chance to get one (I need 3 total but seeing at least one would be nice haha).