Exit Or Skip Loop

I have a For Each...Next loop to read and write data from one workbook to another. Now, it's possible but unlikely that a certain "wellindex" (as defined by the Column A value) occurs more than once in the source spreadsheet, and only the most recent value should be used. And now to the actual question. Currently my macro runs a check to see if the current cell's wellindex has already been used, and if so, then it warns the user of potential double-entry. What I'd like to have it do is have it check whether the current cell's wellindex has duplicates further down (e.g., using a "findnext" method), and if so, then skip to the next cell in the For...next loop. I know that I can exit a loop with "Exit For" but I don't know how to have it go straight to "Next c" without embedding everything in an If statement.

Sub DataImport()
'Define variables
Dim sourcedata, sourcename, originname, sourcedate As String 'filename variables
Dim wellindex, ch4, co2, o2, bal, adj, com As String 'data variables
Dim cor, owp, owp2 As String, overwrite As Integer 'prompting variables
overwrite = 0
'Set up the data source
originname = ActiveWorkbook.Name
sourcedata = Application. GetOpenFilename("Data Output Files (*.csv), *.csv", , "Open the source file").........................