The websites I found are £490 / £507 respectively, have had stock now (checked just now 9:28am) since yesterday about 7pm.
Which means they are not selling out instantly, I would guess the price is too high for scalpers, and that other (people that genuinely just want one) have either found, or are waiting on cheaper sources.
It might be the turning point where competition is actually higher then demand, which is obviously good for us (the end consumer) and it seems Zen 3 AMD CPU's are not going the way of 30xx series Nvidia graphics cards which are of today, an absolute state with no signs of easing.
Fingers cross OCUK come through this/next week with Gibbo's claim of the few hundred as per his post.