Bats

Three colors of baseball bats —- yellow, indigo (not blue), and pink —- can be found in-game and currently cannot be crafted. All rare-colored bats will spawn with a random mod (spiked, bladed, etc).

The most common levels are 45, which can be found at Raider vendors bots, the Sonny in Foundation that sells weapons (the one positioned closest to Samuel’s spot), and the Lite Ally Daphne (the child ally). I’ve personally had the most luck with the Raider vendor in Whitespring mall. 

Along with vendors, bats can also be found in a handful world spawns with very low percentage rate, be rewarded following the triggerable event Collision Course and other events, be in U.S. Government Supply Drops and random encounter supply drops, and be looted from humanoid enemies (super mutants, mole miners, blood eagles, etc.) that have the crown icon next to their names. 

Unlike most weapons, the value of the rare-colored baseball bats increase the lower its level, with level 1 being the most valuable. This Redditor found bats from levels 1 to 15 from Collision Course (also great for farming the Forest Camo Jumpsuit and the Responder’s Fireman set).

There is a visual glitch that occasionally affects the bats, making them appear black while the Current Mods box to the right states its true color, so double check your bats before you scrap or sell them, rather than relying on visual cues. 

Duchess Flame has a comprehensive guide to the various methods of finding the rare colors of bats.