I would bet that Modulus was using the same basic neck, just moving the bridge up an inch and cutting the fret slots to 34" scale.
The only remote possibilities for replacement neck I can think of -
Try contacting Geoff Gould at Gould Guitars
; he's the original founder of Modulus, sold that business many years ago, but still makes similar CF necked basses.
Also try contacting Jerry Dorsch of Graphite Guitar Systems; I don't have contact info, but you can google him and find it. He co-founded Modulus with Geoff Gould.
At least, I would bet that either of these guys could replace your fretboard and fret it to a 34" scale, and relocate your bridge.
That's really a lot of work though, and I'm sure quite a bit of $$$$.....if I were you, I'd try some lighter gauge strings from a few different brands. Circle K strings probably has the most extensive selection of gauges around, and they also have some handy tools on their website for calculating string tension for specific string gauge@tuning@scale length.
Another option would be to get yourself a Modulus Flea/FU 5 string. Same CF construction, 34" scale. Their string spacing is a bit wider at the bridge.