Convert System 7 sound to .aiff file

Does anyone know if there is a way to do this with Applescript?

I think you can do this through any scriptable audio-transcoder-able app, such as Audion or Sound Studio. A quick sample with Sound Studio:

set smil to alias "HD:folder:somefile.sfil"
tell application "Sound Studio"
	open smil
	repeat while not (exists document "somefile.sfil")
		-- wait until opened
	end repeat
	save document "somefile.sfil" in (choose file name) as "AIFF"
end tell