These bulbs are also available in most Electrical wholesalers such as Kellihers, CEF, Eurosales etc. (all are open to the public) - just ask for a 15w Pygmy E14 bulb. Most salt lamps will also take a standard 15w Refrigerator bulb available widely,
Salt lamps require a incandescent bulb in order for their main benefit to work.
By their nature, salt lamps attract moisture from the air. Impurities and particles in that moisture get trapped by the salt.
The warmth produced by a 15w bulb, then releases the moisture back into the air.
As warmth is not produced by LED bulbs, an incandescent bulb is required to maximise the benefits of salt lamps - an led bulb can be used, but it will mean any moisture attracted to the salt lamp will not be released back into the air and mean the lamp will get wet and will require regular drying with a cloth.
Incandescent bulbs will last up to 1,000 hours - approx 6 weeks of continuous light.