Find first blank cell after Auto Filter

Greetings, Gurus.

Suppose I am using auto filter on a range to filter down to only the blank cells in column C, and then I want to enter a formula into all those blank cells. How would I determine the range of the first blank cell? Here's what I have so far:

Sub Macro1()
    Range("C1").AutoFilter Field:=3, Criteria1:="="
    Range("C477").Select 'Needs to be first visible cell after the autofilter is applied.
    ActiveCell.FormulaR1C1 = _
        "=VLOOKUP(RC[-2],'[PLine Listing.xlsx]COM_ REPLEN1677'!C1:C2,2,FALSE)"
    Range("C477").Copy 'Same as above
    Range("C477:C" & Cells(Rows.Count, "A").End(xlUp).Row).Select
    ActiveSheet.Paste
    Selection.Copy
    Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
        :=False, Transpose:=False
    Application.CutCopyMode = False
    Range("A1").Select
    ActiveSheet.AutoFilterMode = False
End Sub

Thanks in advance for any help you can offer.