One of my current gigs is actually a RHCP tribute band. Here's the two setups that I've used that have gotten me closest to that sound.
One was to use my Robotalk with a Pedal Power II using both sag inputs (7&8) and sagging the voltage slightly.
The second, and probably actually closest to the record was to use a Digitech BP80 that my brother was throwing away. This thing is by and large useless as it has 100 or so presets, none of which are adjustable in any way. But preset 4 (at least with my bass, which has a hot signal) nails it. And preset 20 works fine for the Around the World intro so it's the only pedal I bring to gigs with a small stage. Who would have guessed?
I don't know if either of those help you, but the bottom line is that you can get that tone with a few different filters especially if you can sag the voltage a bit. The Bassballs sounds like a good suggestion as well. I haven't tried getting the Sir Psycho with it myself but it is a fairly cheap option and from the times I have played with it, I wouldn't be surprised if you could get pretty close.
Good luck.