A great source for magnets is
http://www.kjmagnetics.com. I know they've supplied magnets to other FRC teams because earlier this season they published in their newletter an analysis of the forces involved in holding a minibot to a pole that was very helpful in choosing the right item. That, and they mentioned that they'd had inquiries from several FRC teams.
They have a wide variety of shapes of rare earth magnets at reasonable prices, including magnets that come with countersunk holes, making mounting on a minibot quite easy. They also provide technical info on their magnets on strength, etc.
To answer the question at the start of this thread, one, maybe two hard drive magnets should be strong enough for a minibot, depending on weight and how it/they are mounted and how close to the pole they are when the minibot is running. But the mounting might be difficult given the shape of typical hard drive magnets. Maybe you could drill mounting holes in the steel magnet support, but don't drill into the magnets themselves. Rare earth magnet material, neodynium, is brittle and can break up into powdery pieces that may be toxic. Rare earth magnets such as hard drive magnets and the magnets you can buy from K&J Magnetics and others are usually nickle plated. You don't want to violate the nickle plating. They are mostly perfectly safe as long as you don't try to drill or machine them. I say "mostly perfectly safe" because there is another danger with strong rare earth magnets. They are powerful enough that there is a pinch hazard when you let flesh come between them and whatever they are strongly attracted and close to. I got a blood blister as proof of this. I was just playing around, but it was an impressive lesson.
There are other sources out there, too. Google "rare earth magnets" or similar to turn up a raft of suppliers. At this point, a prime consideration would be how soon they can get the magnets to you.
Good luck!