Sorry to hear about that Ian, what a drag. Can you tell us the serial number of your '78? (We all dig the details in here.)
You can also kludge together a pretty good +/- 18v supply out of a pile of 9v batteries. In series, two 9v = 18v. Continue the same series with two more 9v and the point at the center becomes 0 with +18 in one direction and -18 in the other. Then if you want any life out of it you can do the same again with 4 more batteries and wire that set in parallel with the first (so the voltage doesn't change but the current available does). If you wanted to go wireless with a Series instrument with the LEDs you could use this method. The back of your strap would look like an ammo belt with batteries, transmitter, etc... which could get a bit heavy ... but it would work.
Good luck,
Jimmy J