In Numbers 3 there is no Paste Special > Column Width.
First note in Numbers 3 that to add columns of the same width as the previous all you need to do is click as shown by the arrow here:
Five quick clicks and you're done.
If you do need to use the AppleScript approach (say you are pasting the width to columns that are not adjacent) then in Numbers 3 the script can be quite simple.
To copy the width to the clipboard:
--copies column width to clipboard
tell application "Numbers"
tell document 1 to tell active sheet
set t to first table whose selection range's class is range
set the clipboard tot'sselection range'scolumn 1's width as text
end tell
end tell
To paste the width to selected new columns:
--sets width of selected columns to value in the clipboard
tell application "Numbers"
tell document 1 to tell active sheet
set t to first table whose selection range's class is range
set selRng to t'sselection range
repeat with c in selRng's columns
set c'swidth to the clipboard
end repeat
end tell
end tell
SG