(XBOX)Big Roy 324's post in About Rime Rounds was marked as the answer
I was able to get it in less than 20 runs on the Valac crossfire spy. I chose that one as it was a little easier for me to cheese.
I would suggest that one or one of the T2 grineer spy's to mix things up.
Also I have a compliaint about the octavia neurphotics on the Deimos survival. Online comments suggests this may have left drop tables after the heart of Deimos update. Yet I haven't seen anything that addresses it.