If you're looking at a 2012 Honda Rancher with only a few hundred miles, it's a good idea to check the tires and battery as they can degrade over time. For the kind of terrain you're riding on, it's best to get a tire with good traction and durability. Popular brands include Maxxis, ITP, and Kenda, but make sure to read some reviews to find the best one for you.
As for where to buy them, you can check out specialty ATV shops, Amazon, Rocky Mountain ATV/MC, or even the manufacturer. Just double-check the size you need before making a purchase.
Installing ATV tires can be a challenge, so if you're not confident in your DIY skills, it's best to have a professional shop do it for you. They'll make sure everything is mounted correctly and that your ATV is safe to ride.