They can't be unlocked at the moment, sadly.
In the Steam version of the game (SuperTotalCarnage!, still in Early Access after two years), those "unlocks" are the evolved versions of each weapon. Supposedly, weapon evolution works like in Vampire Survivors, i.e. you need to fully upgrade a weapon to Lvl. 8, have the corresponding passive equip picked up (different for each weapon; also upgrading to max is unnecessary), and THEN pick up a treasure urn and hopefully RNG favors you and you get the evolved version of the weapon (overwriting the base weapon) as a loot drop. You then upgrade the evolved weapon to Lvl. 10 to unlock it for future playthroughs.
As an example, to upgrade the chainsaw (Moosega) to the Disco Inferno, you need to upgrade the chainsaw to Lvl. 8, have the Lantern in the Hands of the Blind (okay, let's just call it the Blindman's Lantern) in your possession, and then pick up a treasure urn after defeating a boss and hope the RNG favors you.
...Which is what I tried to do, but after repeated failures with it and other weapons I asked a dev and they replied saying that weapon evolution is still not implemented in the GalaCarnage version of the game. So, bummer.