Not so weird. We needed to replace a whole unit because the blokes fixing an air-con' unit, despite having a step ladder, used the loo to get up into the ceiling and subsequently cracked the cistern. :/
If you live in one of the Emaar developments, you can call them and ask them if they have a unit which matches the one you need to replace. Even easier if you have a maintenance contract because then all you will pay for is the unit itself. DragonMart, agree, is also a great place to hit -- they have loads of bathroom vendors there -- but do make sure you have a qualified plumber to do the do, and if you can get a unit which matches the pre-existing ones, even better. :)
Try dragonmart (they sell other bathroom fixtures) or the bathroom shops over near the marriott hotel in Deira. There are probably places in al quoz too.
<em>edited by Cherry ripe on 11/12/2012</em>