Define FirstRow & LastRow in a subset of data

Can you define FirstRow and LastRow functions define a set or group of number? The start and end of a set so in sampledata sheet for column A for numbers = 1 FirstRow would equal A2 and lastRow equal to A8. That would allow me to then know the range of numbers for my PercentRank function.

I have been trying without success. My code represents where I am going but if you have other code please let me know.

This code is attemping to define a values of a group which all have a number 1 as its value and work out the percent rank of values in Column C and return it to column D.

LastRow = Cells(Rows.Count, 1).End(xlUp).Row
FirstRow = Cells(Rows.Count, 1).Start(xlUp).Row
Cellref = ?
Dim myArray (1 to 9)
Dim X as int
X = 1
For Each group In Range("A", Range("A" & Rows.Count).End(xlUp)

            If group.value = "X" Then 
                       PERCENTRANK(Cells("FirstRow, C": "LastRow, C", "Cellref needing loop"))
                    next X
             next group
End Sub

What I am trying to acheive is column D in the Sampledata workbook.

So that PERCENTRANK(Cells("FirstRow, C": "LastRow, C", "Cellref needing loop")) when column A equals 1 would translate to

PERCENTRANK($C$2:$C$8,C2)
PERCENTRANK($C$2:$C$8,C3)
PERCENTRANK($C$2:$C$8,C3)
PERCENTRANK($C$2:$C$8,C5)
PERCENTRANK($C$2:$C$8,C6)
PERCENTRANK($C$2:$C$8,C7)
PERCENTRANK($C$2:$C$8,C8)

And then repeat for each number in column A.