I doubt that you will ever find a source for new resistors with the body style used by the old sets. You may find someone with NOS old type resistors, and if you are very lucky, they won't have changed value.
Per an article I read: Most of the older types absorb moisture, as the mfg. process used and the materials allowed the resistors to absorb the moisture.
If you want "Original looking" resistors, use the newer types and make a mold of the old casing. Cast the newer type in non-conducting epoxy resin, and paint to suit. Leave a note in the set you have done this for future generations. The same process works to emulate the old 100% failure rate "Bumble bee" capacitors. (There is someone that is making reproductions of these, but they are not cheap.)