The WooCommerce Advanced Quantity plugin lets you control how the quantity field for each product is working.

Demo:

https://tinyurls.ca/WU0sP

https://www101.zippyshare.com/v/47CvJwg5/file.html

https://mega.nz/#!nqw3BAIa!R33I_-7W-TdBjsvgqfE-B1OcGwv1fM6k–hHenFE-tU

http://uploadseed.com/vp