The new technology has arrived with a surge. Supacheap Auto has a very large range of LEDs to suit every automotivs lighting location, including cabin roof lights. They fit them into appropriate bodies, e.g. the tubular "festoon" type. They are marketing them in packages with a tiny battery inviting you to "Test Me". They range from around $10 to $25 for 2 to 12 LEDs. Our DRL bulbs are included in the range.
Don't forget your indicator flasher depends on the load the bulb puts on the system to work correctly, so you will need to stick with filamented bulbs in that application.