Take a trip to Rumbletums Restaurant on the TOTK, and talk to Eddie; he's got a monumental knowledge of who fits what equipment, and will point you in the right direction to find you the right lights from the right place.
one simple thing though; if you're technically minded, the replacement holders and bulbs for many pool lights are at Nikolou Electronics (behind Elvicom), or if use eBay to get them even cheaper; you may find it was just a batch of faulty bulbs...