https://www.rockpapershotgun.com/2018/03/14/warframe-celebrates-its-5th-anniversary-with-ninja-loot/ Log in to grab the free loot. There are also many low level missions that will allow you to grab a bunch of semi-rare goodies.
All the Dex weapons you can get from the anniversary alerts are definitely worth getting if you have missed them before. If not for yourself, then just for having extra ones on hand if somebody needs/wants them.
Ah, my mistake. Dex weapons actually can't be traded. I confused them with "special weapons" category which consists of syndicate weapons, wraith, vandal (parts of those) and prisma weapons. Carry on.
