Hi Ester,
There is a lot of procurement planning material around as it is quite a mature discipline in many countries, so it is a little easier to respond if one know what type of research or for what purpose. When researching Procurement Planning in the Public Sector around 2 years ago I found the following countries and sites of some use:

• Procurement planning is quite established in the Public Sector in some of the Australian States, particularily New South Wales (http://www.dpws.nsw.gov.au/Governmen...rocurement.htm) and also South Australia (http://www.statesupplyboard.sa.gov.a...andguides.asp).
• In South Africa, procurement planning is included as part of the Demand Planning process. For more on the Demand Management process look at their national treasury website www.treasury.gov.za under the PFSA and Supply Chain Management entries;
• There has been some progress with procurement planning in Ireland (look under the topic of Aggregation) www.finance.gov.ie

Hope this helps as a start. I have copies of many of the public domain documents on Procurement Planning and can send them to you if needed.
Best regards
ShaunScott, Joburg