Tell him to use 4 separate new caps instead of the multi-section can if he can't find one. He can mount them under the chassis or in the old can if they fit (he'll need to clean out the old guts from the can for the latter). If they are mounted underneath, he can leave the old can in place for looks.
Antique Electronics Supply has some new multi-section can caps; look there maybe you'll get lucky. If not, do the above.