Hey @chibi.nahga.96272! 
Generally speaking, we add them on a rolling basis. You can keep an eye out on our monthly and weekly update threads (see March here: What's New on DC Universe Infinite & ULTRA: MARCH) to see what’s coming up next!
If you have any specific requests, feel free to submit them here: Comic Book Print to Digital Request Thread. All community requests are forwarded to the content team in charge of digitization. 