Light fittings can be tricky to find as there is so much choice. Its easier for me to say where not to buy.
Do not buy light fittings from Amazon or eBay Unless they are made by a recognised company.
Amazon and eBay do not need to abide by the same regulations as stores in the UK as it is classed as a market place, so most light fittings although a lot cheaper are not necessarily safe for installation here in the UK.
