Useful article for discussion on factors affecting supply, see where to find the relevant section within the specification for A Level Economics:
Edexcel spec reference 1.2.4 b) The factors that may cause a shift in the supply curve (the conditions of supply)
AQA spec reference 4.1.3.3 The determinants of the supply of goods and services
OCR spec reference P8 Explain, with the aid of a diagram, how changes in the factors affecting supply will impact on equilibrium price and quantity