public Dictionary<string, Product> ProductList = new Dictionary<string, Product>();
// populate productlist

public class Product
{
	private string m_ServiceProductNumber;

	public Product(string ServiceProductNumber)
	{
		m_ServiceProductNumber = ServiceProductNumber;
	}

	public string ServiceProductNumber
	{
		get { return m_ServiceProductNumber; }
	}
}

public class Item
{
	private string m_SiteId;
	private string m_CompanyName;
	// etc...
	

	public Item(string SiteId, string CompanyName)
	{
		m_SiteId = SiteId;
		m_CompanyName = CompanyName;
		// etc...
	}

	public string SiteId
	{
		get { return m_SiteId; }
	}

	public string CompanyName
	{
		get { return m_CompanyName; }
	}
	// etc...

	public Product Product
	{
		get { return ProductList[m_ServiceProductNumber]; }
	}
}