if you need them to be 3/4 thick couldn't you just buy 1x6 or 1x7 and cut them to 4' long? 1x6 would be a little short on the width but if you got the 1x7 or 8 and rip it to the 6" you need? Shutters themselves aren't terribly difficult to make, the operable aspect makes it a little more difficult but you can find some tutorials online for the movement.