One of the unique things to me about the Alleva J's is that they sound very, very passive and vintage in active mode. I've never heard another active J bass (Fender or boutique) accomplish this, and it is one of the things that IMO sets the Alleva apart (the ability to have the advantages of an onboard preamp while keeping a very passive, vintage tone). Also, Jimmy's single coil pickups are just something.
That being said, a good passive J bass like some of the newer Fenders should get you pretty close to the tone, which again is very 'passive Fender' in nature. You won't get the Alleva fit and finish, nor the unique 'passive sounding active' vibe, but it will sound like a J bass!
If you want an active 5 string, I have not heard nor played anything that really cops that more vintage tone myself.
IMO.