73 280 SEL radio antenna and temperature knobs

I recently bought a 73 280 sel 4.5 (57,000 original miles) from the estate of an elderly couple who hadn't driven at all in the past eight years. The car spent it's first ten years in New Jersey where it developed a bit of rust. Luckily, the rust damage isn't extensive, and now that the car is in New Mexico, it isn't likely to get worse. The body is very straight and the interior is excellent for it's age - the carpeting and headliner look almost new.

After as series of repairs, which included new fuel, brake, and heater hoses; timing chain; radiator leak; air conditioning conversion and recharge; and the rear hydraulic suspension replaced with a spring, it is finally running smoothly, is reliable, and handles well.

Two items still need to be fixed. The first is a broken off Hirshman power radio antenna. I wasn't able to locate one in the Albuquerque area. The second is the temperature control knobs, all of which are plastic and have broken off. My Mercedes mechanic is quoting me over $500 to replace the knobs with after-market ones. Does anyone have any suggestions on an economical but authentic way of replacing these two items? Should I consider an after-market antenna?

Thanks!