Just for the record, you have a 3 piece crankset. What you want is a cotterless 3 piece crankset.

Sheldon recommended replacement spindles intended for italian (70 mm) bottom brackets but I have seen 3 series spindles advertised on a popular website as being appropriate for the switch as well. Trial and error is probably the only way you'll find out for sure what you can get away with. If you have any regular bottom brackets lying around, throw the spindle in there and see if the adjustable cup threads in too far. If not it's your lucky day and any readily available standard spindle will work. If your cups have thin walls you'll need a slightly scarcer italian width spindle, they are harder to find (unless you want ISO taper) but they are definitely out there. If you let me know which you need I'll try to point you towards a source.