I'm at the part where I've been told I need to retrieve an Elder Scroll, and the quest is telling me to talk to the Orc guy that runs the library, in the College of Winterhold; however, he has no relevant dialogue options, only what he can sell me, and nonsense about his side quests to find random books

Has anyone else had this issue? If so, any workaround would be appreciated

This is a bug. If you're on PC, you can open the console and type setstage MQ205 80 to advance the quest properly. It's also possible to continue through Alftand and Blackreach as normal, but you will not have any quest markers to rely on.