I'm going through this now as well. I just removed all the original tack strip material out of the bows and will need to find replacements.
The short tack strips on the ends of the center bows were 1/2" x 1/2". Then the ends were put in a press and smashed together to hold the tack strip in place. That basically changes the width to 3/8" at the top but the bottom is still 1/2". I think the only thing I can do is glue some 3/8" stuff back in. I searched E-bay just to see what sizes are available. I did find some 1/2" x 1/4". I wonder if that would work for the rear bow? I'd just have to glue two pieces together.
What are you planning on using to attach them? Glue? If so, what kind? I also thought about letting the upholstery shop that will put the top on, pick whatever tack strip they wanted since they have more experience than me.
My side tack strips weren't that bad but the factory installed them before painting the bows. I could see rust showing on the sides so I wanted to clean it all out and paint it before installing new one. You can kind of see how the ends were smashed together to hold the tack strip in place.