Well, being able to restore the Falmer so easily wouldn't make for a very good mod. And you need to own Riften which will allow you to start the Trinimac event chain.
As for the Schematics, they are most commonly found in the various dwemer ruins that can be explored throughout Skyrim, if you haven't got any from that then you are incredibly unlucky im afraid. Also, the requirements for the Vyrthur/Auriel's Bow event to fire are:
- Be Gelebor
- Own the Chantry of Auri-El
- Vyrthur is a secret vampire
- Vyrthur has trait "On Mission"
It should trigger within four years, though that is not guaranteed. If you use the family focus the chance for it to fire is doubled.