In Numbers 4.0.5 I figured out how to do a basic lookup and select the found cell.
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# Look Up a Value in a Given Document
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tell application "Numbers"
tell document "Some Document"
tell active sheet
tell tables
set theCell to first cell whose formatted value is lookup
if theCell ≠ {missing value} and length of theCell = 1 then
set theCell to item 1 of theCell
set theRow to theCell's row
set selection range to theCell
end if
end tell
end tell
end tell
end tell
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TIA.