Exterior Door Adjustment Strip

You will need to contact a Therma Tru dealer in your area to get that oak threshold for your door. If there's nobody near you, you might be able to have one made at a mill work wood shop. 

If the screws are still in good shape you could use WD-40 to loosen them up. I had to do that on my adjustment screws at home. It did take a few weeks to lubricate them, but they eventually come loose.