The information you are looking for is given in the SD card physical layer specifications, published by the SD association. The SD association only makes the simplified specifications available from their website (see https://www.sdcard.org/downloads/pls/). Unfortunately, the simplified physical specifications don't give the details of the contact locations: they only give the overall physical dimensions of the SD card.
And, to quote their website:
Simplified versions of selected SD memory card specifications are available for download by developers. To get access to the full specifications, simply [sic] join the SD Association.
Of course, joining will cost you the ridiculously low amount of 2,500$ (annual fees).
Fortunately, internet is a great place (for illegal things) and you can easily find older versions of the specs anyway. I'm shamelessly giving a random link because I find it unacceptable that you should pay for that (and giving a link isn't forbidden by law, only the owner of the linked website is doing something prohibited here):
You can find what you need at page 107.
Alternatively (if the link above goes dead due to a cease and desist letter), you could find the information in some detailed datasheets from various SD card vendors, for example at the link given by @TEMLIB (in the comment above):