There’s not a part number for the track piece you circled. At least not that I was able to find. I replaced the broken pieces on both sides, with a kit that had all the pieces, from tgautomotive.com. However a couple of weeks ago when I was telling another member about the kit that I bought, their website did not show any kits for the GMT800 platform. When you click into that section of the website it was just blank. So I’m not sure if they’re not making them anymore or were just out of stock, but I would suggest emailing their customer service and asking about it. That was the ONLY place anywhere online that I found the correct pieces. All the other repair kits listed on Amazon and eBay were for 2007-2014 models which is the GMT900 platform and I’m not sure if those pieces will fit or not. I can’t answer the bit about the seal that goes around the glass as mine is fully intact and did not need replacing. For that I would suggest checking out GMpartsdirect.com as many parts can be had from there and most of the time part numbers as well.
@915_Tahoe is our resident part number guru if I’m not mistaken?! Maybe he can chime in with a suggested source or a part number for that seal.