An implementation I made a while back of the repmat() function since the API I was using did not have it implemented it at the time. I would love to know different ways of approach this problem, it was meant to work with MathNetNumerics library matrices but it can be adjusted to fit a 2D array of any type (not just Doubles).

repmat.vb

''' <param name="matrix">The matrix to be tiled</param>
''' <param name="row">The row dimension of result matrix</param>
''' <param name="column">The column dimension of result matrix</param>
''' <returns>The tiled and replicated matrix.</returns>

Function repmat(ByVal matrix As Matrix(Of Double), ByVal row As Integer, ByVal column As Integer) As Matrix(Of Double)
    ' Initialize the proper dimensions of the new matrix
    Dim result As Matrix(Of Double)
    result = New DenseMatrix(matrix.RowCount * row, matrix.ColumnCount * column)

    ' Used to keep track of indices
    Dim m As Integer
    Dim n As Integer

    m = 0

    For i As Integer = 0 To result.RowCount - 1
        n = 0

        For j As Integer = 0 To result.ColumnCount - 1
            result.Item(i, j) = matrix.Item(m, n)
            
            n += 1
            If n = matrix.ColumnCount Then
                ' n is equal to number of columns of matrix and time to reset
                n = 0
            End If

        Next

        m += 1
        If m = matrix.RowCount Then
            'm is equal to number of rows of matrix and time to reset
            m = 0
        End If

    Next

    Return result

End Function