So issues. I want him as a follower, but first I need to do his quest.

However, he isn't offering it for some reason, no topics at all about it. I might have accidently declined him in the past. Can I get it back? Is there a console command to force it?

This is a Radiant AI quest. Radiant AI can only give you so many of a similar type of quest at one time. That means if it wont show up in conversations when you have another similar quest blocking it. You will need to do any similar sidequests or miscelanious quest in your journal before it will become available. Its probably another fetch quest, something like the sword recovery one from the Smith in Windhelm thats in the way.

This is somewhat embarrasing, but it turns out I apparently had already accepted the quest a long time ago, as it was buried deep within my Misc quests folder

Sorry 'bout that all