Well, here's a bunch of listings on Bricklink that seemed to stand out.
Here's a Yo listed as the color being not applicable on Bricklink. Perhaps it's a GPKK?
And this doesn't look much like a metallic silver Za Krana. Probably nothing special, but...
And again, here's a strangely out of place Xa Krana in the metallic silver section. Again, it's probably nothing but it's worth a shot, I suppose...
Yet again, an out of place Krana, this time a Ca, in the metallic silver section. This seller either has mislisted these 3 with the wrong pictures/category, or perhaps he actually has some GPKKs.
Ok, here's something that might actually have a good chance of being GPKK! A pearl white Krana Su? Pearl white? Sounds like the color of a GPKK! Or it could just be another mislisted Krana, seeing the picture, which may or may not be the default pic. But I think this one is definitely worth contacting the seller about.
Not sure if you've already seen this, but this guy definitely has some GPKK... it's only a matter or whether or not he wants to sell them.
Also, if you're really desperate, you could always try asking every one of the sellers on Bricklink in the "pearl light gray" & "pearl very light grey" categories on Bricklink.