Mod Question(s)

I was wondering if it is possible to get synergy mods outside of the Synergy Mod Cache? Also, has anyone confirmed that the highest mod is blue?

I have gotten synergy mods from side quests, sometimes being lucky enough to score a sweet blue mod with scavenger synergy for example. As far as mod rarity, I too am interested to know. So far I have just been stocking up on all the blue mods I can find.