Piaf: The truth is this Beogram 4000 is so extraordinarily beautiful that it bothers me that it has black electrical tape holding on a cheap US electrical plug and RCA connectors.
As to the power cord, I'd just get a modern cord with a molded plug, which should be available in any electronics or hardware store. Even the "correct" old cords may have become brittle with time, and any electrical tape fixings can become outright dangerous. Imagine the tape losing its grip with time, exposing a live wire, and someone vacuuming behind the shelf while possibly even leaning on the heating radiator. Even the original power plugs, which often were very hard plastic and held together with screws, can be dubious at best.
(and after all this, guess how I have my originally UK Beogram 6000 rigged up at the moment?)
The DIN cable is a little bit more difficult, since it has to have shielded audio connections and not just some mock-up which happens to have the right pins connected. It's also difficult to construct properly yourself as the connector has so little room inside and the cable can't be too thick. If you can get the donor deck for $10, I'd take it; I'm sure you can sell or use many other parts of it too.