Status Graphite sell custom double ball end sets, available gauges from .020 to .135. I recommend choosing a .135 B for a nice tight string. If you like the idea of equal tension on each string the gauges to order are 135 100 75 55 40
http://www.status-graphite.com/statu...ndex_home.html
From the menu go to 'On-line Shop' > 'Bass Strings' > 'Double-Ball' > 'Double Ball Custom Sets'
"DOUBLE-BALL STRINGS :
Round wound, half-wound, flat-wound and vintage black nylon strings are all available.
All are hand-wound and manufactured to the industry standard double ball string length
of 908mm (35 3/4") between the inside of each ball-end.
They will work perfectly on all Steinberger and many other headless basses."