Oh hey, guess what-- not even the most perfect original Mutron III sounds like that!

Check out some threads about Bootsy's rig. In order to get that tone, he is splitting his bass signal into multiple channels (different pickups, different frequency ranges) and running
each channel through
its own filter or other effects. Bootsy's tone is literally
unattainable unless you (a) have a lot of money and a roadie, or (b) lower your standards to a sound that you can convince yourself and the audience is "close enough".
Once you've lowered your standards the way we all do

, you'll find that the tone quality of the Mutron III may not be worth the expense and the practical troubles of having it, compared to the other filters that have 80-90% of the tone and only 10-20% of the hassle, at 30-60% of the price.