I bought the book "Physics for Mathematicians I" by Michael Spivak (http://www.amazon.com/Physics-Mathematicians-Mechanics-Michael-Spivak/dp/0914098322), have worked through quite some chapters and love it. I am really looking towards the sequel(s) and wonder how far the author, secretive as usual, has gotten with them. Do you have any information on this?
Update: It's very sad to hear Michael Spivak has passed away last year, thanks you ho-boon-suan for letting us know.
Unfortunately, as shown in the link by ho boon saun in the comments, there probably will never be a "Physics for Mathematicians II" by Michael Spivak since he passed away before it got published/fully written - unless someone who personally knew him, and had access to his belongings, could publish his unfinished drafts, which seems unlikely at this point.
On a positive note, as mentioned by Tarc in the comments the first book is rather expensive and was inaccessible because of the cost. However, the Internet Archive has scanned the book and made it freely, publicly accessible. So while we'll probably never get a second book, it can be positively assured that the same book that gave you, and others, joy has been made more accessible for future students.