Brake pads are pretty generic (read available). There have been changes during the years, so best bet is to simply take your old ones into a shop, and find a cross reference model/brand that works for your application, and then remember it. Gas Gas, Honda, Suzuki, Yamaha, all use the same pads in some application. From memory, there was a change to the rear calliper in from 09/10 with Gas Gas going to a shorter rear pad.
Brake levers, never sourced. Not sure.
Bearings, all available through the local store. Allied bearings has served me well. Usually take the old bearings and seals in and they'll match them up. Once you know your parts add to your own list. I generally buy doubles and keep them as my spares.
Not sure about the 4T range, but on the 2T the kick starter crosses over with Yamaha (most models).
Haven't looked into replacement/after market brake pedals or gear shifters. I think a Yamaha brake pedal could work with some minor modification.
Chain sliders and guides are available OEM, TM Designworks, or Bullet Proof. TMD are pricey, but last really well.