Well I "froogled" the Asus P5K and came up with this. Now eWiz has a listing for it but when you click on the link the eWiz site directs you to an "out of stock" item. One of the other e-sellers had an ETA of May 11th. FWIW, and this is a total guess, I would imagine you will see several P35 boards by this weekend at the latest.
Edit to add:
Hmmm... now (5/10, 12:30 pm CST) there isn't even a listing for eWiz when doing a froogle search. That can't be a good sign.
My understanding is the the P35 boards are not supposed to be released until May 21st. There are boards out there but Intel has a NDA that is currently holding them back until the chip is officially released. This site is listing the board in stock.
I think the boards have already made it to some reviewers but once again they a refusing to post the results until after Computex.
A shop here in Belgium had 10 in stock on May 8. I've seen one review (of a gigabyte MB) which turned out to be slightly slower than the P965 counterpart.
Still, it'll should accepy the Penryn generation CPU's, which is what I'm after anyway.