I would use a filter instead of a find loop:
Sub tgr()
Dim rngVis As Range
Dim VisCell As Range
Dim sFind As String
sFind = InputBox("Please enter the Column Name to find matching Source File Field Name.")
If Len(Trim(sFind)) = 0 Then Exit Sub 'Pressed cancel
Application.ScreenUpdating = False
With Intersect(ActiveSheet.UsedRange, ActiveSheet.Columns("B"))
.AutoFilter 1, sFind
On Error Resume Next
Set rngVis = .Offset(1).Resize(.Rows.Count - 1).SpecialCells(xlCellTypeVisible)
On Error GoTo 0
.AutoFilter
End With
Application.ScreenUpdating = True
If rngVis Is Nothing Then
MsgBox sFind & " could not be found."
Else
For Each VisCell In rngVis.Cells
MsgBox "Source File Name: " & VisCell.Worksheet.Cells(VisCell.Row, "L").Text & vbNewLine & _
"File Column Name: " & VisCell.Worksheet.Cells(VisCell.Row, "M").Text
Next VisCell
End If
End Sub