Are you thinking of a digital or analog filter? I'm thinking the source audio spectrum would be a good replacement size if you don't mind digital.
Funny you should mention it! Wholly without intending to, I must have willed a pedal sale into existence; found the PERFECT fit both in terms of size and tone on my local Kijiji late last night. One of those can't-pass-up-the-deal types, despite wanting to prioritize other stuff!
The Spectrum was on my list, as was the Josh Wah (perhaps too large), and the Fwonkbeta. But despite being a bit of an odd duck, I wanted a Seamoon Funk Machine. Not really a super versatile filter, but the sound it *does* do covers easily 90% of the material I need it to, and the rest I can definitely get close enough to. Very MuTron-ish, thick, analogue, and percussive. I know I'm honeymooning, but dang this thing is a fatty. Pairs brilliantly with my OD and octave, too.
Will admit, you've caught me off-guard; no pics yet since I wasn't remotely anticipating this purchase (so, like, did it even happen??)!