Well, WDC has now updated their 65XX.COM website. They have some of their early SXBs available. You can fill out a developer form and you might be selected to get a free board to develop with:
http://65xx.com/Developer_Products/SXB-Boards/ Also, they've updated their description of the 65C51 slightly, now saying "Not a direct replacement for legacy systems":
http://65xx.com/Developer_Products/65xx-chips/ Unfortunately they have not updated their datasheet, so it doesn't cover the xmit bit bug in the errata and still list it as a replacement for other 6551 chips. I guess I'm a bit unclear on the legacy comment. I do hope they manage to get a new run of working chips soon.