There's a company named L'Arsenal that sells a lot of naval accessories in various metric scales. Highly recommended. I looked and they don't have helicopters in the scale, basically because neither the Yamato or Bismark did, but they have a LOT of Photo Etch railings, stairs and ladders, both kit specific and generic. That could really add to your model.
Also check out Shapeways. They have a super eclectic product line, basically they connect needs with resources in the 3D printing world. They add new stuff on almost a daily basis.
https://www.shapeways.com/product/FXCTEQ7H7/011d-a109-1-200?optionId=41015775&li=marketplace
Good luck