There are a few ways,there are some available on e-bay from time to time,some being the aftermarket types not "made or licensed by fender made", Then there are some sold by "licensed " dealers claiming to be leftovers from repairwork done to a Fender bass/basses which a "true" decal/decals were sent to complete the repairwork done by a "Licensed" Fender repairman to a bass that was a "Licensed" Fender bass recieving either a Genuine neck from Fender or a Aftermarket "Licensed " by Fender neck.
I did some apprentice work under a Licensed(I hate this word) Fender warrenty/repairman and witnessed Fender sending an Authentic headstock decal to complete a repair,either a new neck from them or a Lic. distributor or repairs to the original neck that required installing a new decal because of damage to original one during the repair,BUT know this it was a tedious endevour to get this decal,it had to be proven un-deniably that the bass or guitar was in no question a true Fender and the new parts were also no doubt a Fender or a Lic. Fender part that is to be used,AND the repair being done was liable under the warrenty.
So if your need is legit contact Fender and start the process,if otherwise check E-bay they are usually there.
BOOMSHANKA: "May the seed of your loin be fruitfull in the belly of your woman"
Neil quoted from the "Young Ones" MTV Sketch series.