The weight these can handle wwill depend on the material used and the width of the shelves. MDF will be more prone to bending than ply.
You can buy the support pins in many DIY outlets, you can also get a (bottom half of page) to make acurate drilling of the holes a lot easier. Could make up a template yourself without too much bother though.
Main thing to get right is to make sure the drill/ router bit you use is the correct size so that the pins are a cosy fit.
Leo