Here's a link that might help. I was also able to order thresholds similar to pro-bilt through home depot.

When replacing, before installing the new, you might want to consider applying self adhering flashing tape such as protecto wrap as well as silicone caulking before placing the new to dam and keep water from getting under the threshold.

Here is a link that might be useful: replacement threshold

Sierraeast: Thank you so much for your kind advise. We were able to find the right size thresholds at a home improvement store locally and have purchashed the silicone caulking. You have given us great advise. We will however have to remove on of the french doors to enable the threshold. We are letting the area dry for a couple of days and hopefully, this will be our weekend project. Thanks again

i also have probilt french doors and my threshold needs to be replaced because of the rain. bought the door from lowe's but like you, can't find a new threshold. I also have a hard time, sometimes, closing my door because of the rotted wood! Somebody should know something about this company.

Linda, we finally found a metal threshold at a very small home improvement store. (Who would have thought a little store would have what we needed and Lowes did not) It took some work to remove the rotted wood and install the new threshold but we did it. Try looking at some of the smaller home stores in your area, you will be surprised at what you can find. Good luck, I feel your pain