I don't have anything that great to add but I have had an everest rucksack more or like this, but without the accent colors and buckles (has more modern/basic clips/zippers/magnet clasps) for going on 10 years. It doesn't get daily use but it has held up well so far and been on some big trips with me: https://everestbags.com/Item/CTRS01
I also have had decent luck with Fox Outdoor stuff. Both from the same local surplus store actually. But its not that much more expensive online
You probably want something bigger than anything I have though, so ymmv