One significant barrier to searching Addis Zemen newspaper archives is the script. Amharic is an abugida (Fidel) with over 250 characters. Optical Character Recognition (OCR) for Amharic is still in its infancy. Consequently, you cannot simply "Ctrl+F" for a word in a scanned PDF like you can in English.
If you are at a university, start here. The CRL holds a massive microfilm collection of Addis Zemen from 1941 through the 1990s. Many partner universities (in the US and Europe) have access to digitized versions of this microfilm. You can scroll through PDFs of the actual pages, albeit in grainy black and white.
Historical government announcements and national policies.