Are there any Audio Unit V3’s specifically made for bass that I can buy?
It's not 'specifically' for bass (in that you can make awesome lead, percussive or FX tones too), but Viking Synth is definitely up there with the best the platform can offer for bass tones. Loads of great presets too.
Not in B3, it doesn't support presets.
I 2nd Bassalicious 2.
I port the electric bass Gadget into BM3 when i need a good bass sound. The quality is surprisingly good. Think it's called Gladstone.
There's also iFretless Bass.
There are several different bass sounds i.e. not just the sound of a fretless bass but has actual fretted bass sounds.