BKP's own 550K pots are very, very good. However, any 500k pot will do fine.
The thing is just, that Ibanez use smaller pots, who are a bit narrower than the usual ones you can get everywhere. Don't know if BKP have them in this size, but seeing as a whole cr@p-load of BKP pickups end up in Ibanez guitars, what with the djent fade and everything, I'd be surprised if they aren't available.
Also, check the grounding, and the soldering all round.