Are you missing the entire awning or just parts of it? You can buy complete awnings or just parts of them. Like you could get an awning tube and fabric if you have the arms. Or just the fabric too.
I think your best source would be to check your local RV dealer or Camping World. The factory awning would have been an A&E awning by Dometic, but I prefer Carefree of Colorado awnings. The company is a great company to work with, and they have a much superior product, even though it might cost just a little more. The parts aren't compatible I don't think, so if you have some parts already, I don't think you can mix them. Sometimes you can find used awnings, but it's rare and they often need something (usually fabric). Finding the exact size you need will be challenging too.
If you are heading out I-80 anytime soon, you could check out the RV surplus places around Elkhart...you might be able to find one cheaper there than say a Camping World, but it wouldn't make sense unless you were heading there for other reasons.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR