Any copper wire will work.
Just go to Dick Smith's.
Go to their self-service wire section and look for their skinniest
thinnest wire, its only about 20c/metre & comes in 6-8 colours.
I'd usually colour code it too.. eg
black for 27Mhz
purple or grey for 29Mhz
white for 40Mhz
If you haven't lost the broken part of your old wire, just measure
the whole lot and put on a new wire of the same total length.
If you can't find the broken bit, just find someone with the same
RX on the same band whose wire is *known* unbroken and
measure that length it is.
Next time you're out with your car, best to do a Range Check.