Door threshold seal Stanley
Thanks for reaching out to us. This is a bit of a weird one. I'm afraid we don't have any kind of weatherseal that functions how this does. What's throwing me off is that the seal part itself (what I presume to be the ribbed stem on the right) is facing the same direction of the kerf (the arrow shaped stem in the middle). This is very uncommon. Nothing in our inventory quite works this way.
I'm not sure where you may be able to find this, especially if this is an older door. I think your next best bet would be a local shop with some history in the area, like a mom and pop kind of hardware store. They may have an idea what this could be if they're familiar with homes in your area.
I'm sorry that we can't be of more help.