If you want an alias rather than a symlink the simplest way is:
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set targetFolder to alias ((path to home folder as text) & "test_directory:KM_TEST:")
tell application "Path Finder"
set selectedItemList to selection
repeat with theItem in selectedItemList
set (contents of theItem) to POSIX path of theItem
end repeat
end tell
repeat with theItem in selectedItemList
set (contents of theItem) to alias POSIX file theItem
end repeat
tell application "Finder"
repeat with theItem in selectedItemList
make new alias file at targetFolder to theItem
end repeat
end tell
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This will handle one or more items selected in Path Finder.
The scripts Tom has pointed to use ASObjC and the File Manager and will be faster for multiple items, although they'll take some modification to do what you want.