Dim r as new Regex("[àèìòù]")
dim mc as MatchCollection =r.Matches("tuo testo")
for each mc as Match in mc
..
next

Public Class Persona

    Private m_Nome As String
    Private m_Cognome As String

    Public Property Nome() As String
       ...
    End Property

    Public Property Cognome() As String
      ...
    End Property

Dim listAccentate = From p As Persona In lista
Where Regex.Matches(p.Cognome, "[àèìòù]").Count > 0 
Order By p.Cognome Select p

Where Regex.Matches(p.Cognome, "[àèìòù]").Count = 0