Don't worry too much about the electrical specification of the LEDs if you're replacing boggo standard ones. Just find some replacements that are of the same colour and package for the ones you're replacing. For example the LEDs in your stereo might be standard garden variety 3mm or 5mm package LEDs, or might be rectangular packages, or... depends what you're replacing.
Oh. Are you sure you're replacing LEDs? Rather than tiny 12V bulbs as used in a lot of stereos? Or perhaps they're LEDs with integral resistor? Use a multimeter to test what voltage is being applied to them.