I suppose that depends on what you mean by "just long guitar strings". That's pretty much what bass strings are.
Piccolo strings are extremely light-gauged bass strings, meant to be tuned much higher than regular bass (usually an octave higher, but that's not carved in stone). D'Addarios for instance are
G .020
D .032
A .042
E .052
This is roughly the same as the octave strings on an 8- or 12-string bass. If you want deeper octave strings, just get thicker gauges, nickelwounds.
juststrings.com is a good place for strings, and they have several 12-string sets. Also, try
12stringbass.com.