China based Asustek subsidiaries Pegatron and Unihan are supposedly new OEM manufacturers for the Microsoft Xbox 360 reports Digitimes.

The deal would have a production volume of 500,000 Xbox 360 consoles per month.

Taiwanese Wistron, who was the original OEM for the Xbox 360, wants to drop it because of too low margins according to the article.
There is no official statement of this, so take this information with a certain suspicion.
Microsoft was blaming supply issues for the Sony PS3 beating the Xbox 360 sales in February. Maybe the OEM issue has something to do with that.

In case you need an Xbox 360, the Xbox 360 Arcade is in stock on Amazon.com.