Those Sachs freewheels were sweet. Someone somewhere may have replacement cogs for it, but I haven't seen any in years.
How about picking up a more easily available 13-32 freewheel instead (like
this), then changing your big chainring to something 4 teeth bigger? You'd maintain the gear ratio you like that way. Only concern is that your front derailleur's tooth capacity may be exceeded, requiring a bigger small (and ideally the mid) chainring too.