Search outlook address book from VB.NET

[seraieis]

I'm trying to search the global address book at my company (over 56,000 entries) based on a user name input into a text field. Is there a built in serach method that I'm missing, or would I have to sort the entire list and use a binary search?

        Dim o As Outlook.Application
        Dim ns As Outlook.NameSpace
        Dim al As Outlook.AddressEntries
        Dim entry As Outlook.AddressEntry

        o = CreateObject("Outlook.Application")
        ns = o.GetNamespace("MAPI")
        al = ns.AddressLists.Item("Global Address List").AddressEntries

        'sort and search