I've found one excellent source for high resistance wire can be found
at the thrift sto 5$ Toasters.

At the former AT&T High Seas site at Ocean Gate NJ that I am
associated with they terminated rhombics with some kind of wire (looks
like shiny aluminum wire) in the form of an open wire transmission
line. It comes down the pole and then runs back toward the feed point
near the ground, then turns and comes back the whole length of the
rhombic, and does this 2 or three times - a lossy transmission line I
guess.

Rick