Tin is actually pretty easy to get if you know where to look. I just hit 170 and have really gotten into Iron Deposit's having found a good location to grind & mine.
Good spots for Tin are: Loch Modan (East side from Mo'grosh to Farstrider's Lodge), Wetlands (Spider Cave), Redridge (zone-wide...just run the mountain areas), and Westfall (there is a Quarry by the Coastline mid-zone on the West, lots of good Green-farming also if you're into that). Tin still gave me skill-ups in the mid-160's, so it's viable to just get and sell if you aren't using it around then. 160-170+, you pretty much have to go for Iron and higher for Skill.