You probably won't find one. You may be able to contact an RV salvage yard to see if they have one, but I think that would be your only chance. I haven't seen any reproductions on the market.
Many people have modified them to use some sort of roller catch, newer style screen door latch, or a magnetic catch. Assuming it was just your tabs that were broken, you shouldn't have a problem still using the slider. If that slider is broken/missing, you can probably get a newer style one from an RV dealer and it'll work to block the hole, though it will be a little wider than the original.
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