https://www.dell.com/support/home/en-us/product-support/product/optiplex-3060-desktop/upgrade 

Link is the closest thing I could find to a parts list   Enter service tag into the Dell site (link) and it should show you parts and accessories   Just be sure not to post service tag here (publicly).

I haven't seen much of anything for a card reader that will fit in a DVD slim bay.  They're usually the size of a floppy disk drive.  If @redxps630 can't find the part, I don't know who can.

Thank you very much @redxps630 ! So it's p/n 59MR7 for MT.

correct.  how to install

#13 Card Reader Connector (Card Reader)

#4 Memory card reader (optional)

I found the same part, but thought it went in DVD slim drive bay, so didn't think it was the right one.  Didn't know card reader is one slot in the 3060, and now I do.  Also didn't know it was an optional part.  Seen those slots before not knowing part is optional.