I do a LOT of Restore Missions, well mostly those! & I'm continually finding Tungsten Carbide during these Missions.
So many now that I'm limiting my inventory to 25.....rest get either traded or just sold.
Make sure you do different Restore Mission sites & make note of which type they show up most in ie agri sites, mining sites, Industrial sites, military sites etc.
Then keep going back to that site if it shows again in the Mission board.......I find there's a good chance of returning back to the same site time after time on subsequent Missions.
Sorry I can't say which site type exactly, as I'v not been specifically hunting TC's now for ages & I'm just moving from one Civil Unrest System to another, doing 2-3 Restore Missions, then moving on.