Weatherstripping On Old Vinyl Window Sash

I'm afraid I don't recognize this weatherstripping style. It reminds me a bit of our 58-171 or 58-182, but the design is still a little different. 

For now, review both of the products I just mentioned to see if you could use either one as an alternative. Size will be the major determining factor. I'm also concerned about the orientation of the bubble; it looks like yours might be opposite the T slot, where as ours is parallel. But it's admittedly hard to tell from your photos.