230mm fans

So I bought these cases for our new desktops last year which each have two huge 230mm case fans.

And mine have gone squeaky; I disabled them for a while, but now my back 120mm died (leaving me with just videocard/cpu/powersupply fans). I can replace that, but I'd like to replace the 230s while I'm at it.

Anyone know where to buy a 230mm/23cm case fan? Both CoolerMaster and Thermaltake sell cases with such fans, but I can't find replacements.