Where can I find the Sifre on the book of Devarim online in text form (as opposed to Pdf)?
The commentary of the Netziv would also be appreciated.
Sifre (on Bamidbar and Devarim) https://he.wikisource.org/wiki/%D7%A1%D7%A4%D7%A8%D7%99
Netziv - assuming you mean HaEmek Davar (and not Davar HaEmek or one of the others), Sefaria has most of it: http://www.sefaria.org/Haamek_Davar_on_Genesis http://www.sefaria.org/Haamek_Davar_on_Exodus http://www.sefaria.org/Haamek_Davar_on_Leviticus
Bamidbar will be coming in the next week or 2. No word on Devarim yet - we need to locate a good scan first. (Or a book we can scan).