That sounds like an interesting instrument Dave, so I've done a little quick research on
your behalf. I don't know the Esraj but I am familiar with Ustad Sultan Khan playing the
Steel strings for guitars and similar are made from Piano wire, which
is also known as spring steel. The obvious source would be guitar string manufacturers, so
in the UK Rotosound
are the obvious people
But if you want to shop around, Google for spring wire
, I don't know whether
that search will work with the link, but if you use the term for your own search you will
find plenty of suppliers.
And to help your search, some of the suppliers might
list the wire by AWG (American Wire Gauge) or SWG (Standard Wire Gauge). AWG28 is 0.01260"
and SWG30 is 0.0124".
Hope that helps Dave, and let us know how you get on.
When the going gets weird, the Weird turn Pro.