I want to unlock new weapons for multiplayer but I don’t have gold so I can’t level up in matchmaking. Is there a way to level up SR offline so I can unlock new weapons?
What would you use the weapons for? Anyway I assume that if it’s anything like Reach, you should be able to gain credits and rank up offline through Campaign and Custom games.
Not campaign.
Waypoint restricts access to non gold. Maybe use the web version and use codes.
I’d like to say Spartan ops but it’s only gold…
Do forge and end the game and continue it every few minutes.
Or just buy the Champions Bundle and get weapon skins for every loadout weapon, granting you access to them all. 
You can also create custom gametypes with preset loadouts that have the options you want to use.