do you know where I can purchased a controller like the one above. Thats exactly what I need.There is - depends on the approach you choose, of which there are several - probably boils down to complexity / cost in the end according to your requirements.
For example the motor control in the following link uses the motor back EMF to sense & control the speed under varying loads.
http://www.siliconchip.com.au/cms/A_110145/article.html