Yes, they're old, very old but they still sound great. But unfortunately my receiver went kaput. Any suggestions on a receiver to power the 4 ohm speakers? Or a suggestion on how much power is needed?
How much depends on several factors; how big is the room where you listen? how loud do you play your music? what type of music do you listen to? In a receiver I would say you need to be in the 65-75 watt range to get the quality of power you'll need. More watts won't necessarily sound better, better quality watts will sound better.
Most modern receivers won't care for the low impedance and low sensitivity of the Polks. You'll need to find a receiver that does not warn you about low impedance loads and preferrably one that does not rely on load switches to operate low impedance loads.
If you don't need a tuner, you'd probably do better looking at integrated amplifiers which are the basic components of a receiver minus the tuner. Integrateds tend to have somewhat better quality than most receivers. If you can't find any decent shops in your area caring integrated amplifiers, check out Audio Advisor online.