The official T-Mobile 1.6 (Donut) OTA update link has been captured and here is the link directly to the official update file. The file is the update for existing CRC1 users so be sure you have the CRC1 update before installing this.
From everything I have read, This is the update file for the T-Mobile G1 only, no MyTouch3G support.
I also took the liberty of downloading the file onto AndroidStory so you can get some high speed download goodness here.
Remember, that this the official T-Mobile upgrade file for the G1 ONLY and does not have root or any of the other custom ROM enhancements.