Surprisingly difficult to get information about this. I've done a fairly exhaustive search. All I can come up with is the webfonts API.
https://developers.google.com/api-client-library/java/apis/webfonts/v1
How would I add, say, all 600 fonts into my Android app? Apps such as Fontasy do this well: https://play.google.com/store/apps/details?id=com.youthhr.fontasy&hl=en
You can find all Roboto fonts on this site where you can also download them (a .zip file containing several .ttf files).