As far as I know there are no companies that make an alien covenant plushies. The only alien plushies that ever existed were made several years back. The toy line included a facehugger, chestburster, Queen Chestburster, and egg. NECA did release a few alien plushies recently, a facehugger and alien.
If you want to settle for a replica Hollywood Collectibles should be releasing something soon. It will possibly be the neomorph and protomorph offspring.
If you really want a plushie from alien covenant ask the guys over at NECA if they are thinking about it since they do make alien plushies