We lost the assemble accessary of cassina sofa model 348 Notturno A New York. How to order it and where to buy?

no
you have to feel furniture to see if it is comfortable as you cannot get that from a photo
Another thing not considered
buying on line is well and good but the freight costs generally make the goods more expensive and
if it is not comfortable---tough -- you cannot send it back for a refund

then call the place you bought it from.we do not have them here.

What is the make and model number?

I suggest for you to contact the store you bought the sofa from and ask them for contact information for the Thompson Company. I'm sure they will be happy to send you assembly instructions either by mail or email.

Yes - before you buy a sofa bed make sure that the mechanism for opening and closing is demonstrated to you and that you then try it out yourself.

No need to worry, Ikea keeps online copies of all assembly manuals online. I found the one you are looking for - http://www.ikea.com/assembly_instructions/tidafors-armchair-2--and-3-seat-sofa__AA-492178-3_pub.PDF

The Ikea website has copies of all of their product assembly manuals online. I have found the one you are looking for - there are 3 parts to the assembly.

http://www.ikea.com/assembly_instructions/beddinge-sofa-bed-mattress__AA-65114-4_pub.PDF

http://www.ikea.com/assembly_instructions/beddinge-sofa-bed-rame__48ZM02_PUB.PDF

http://www.ikea.com/assembly_instructions/beddinge-three-seat-sofa-bed-cover__AA-203737-4_pub.PDF

I have found you the assembly instructions from the Ikea website - it has two parts; one for the chaise section and one for the one-seat section of the sofa.

http://www.ikea.com/assembly_instructions/kivik-chaise-longue-frame__AA-449713-4_pub.PDF

http://www.ikea.com/assembly_instructions/kivik-one-seat-section-frame__AA-449715-3_pub.PDF

I found a place for you that is located in New York thatwill pick up, repair and deliver your sleeper chair for a low price:http://newyork.backpage.com/HomeImprovement/furniture-repair-disassembly-assembly-leather-couch-fabric-sofa-chair-sleeper-mechanism-wood-restore/12247233

I'm supposing by eyepiece you mean the rubber or plastic eyecup. The eyepiece is the whole unit that contains the lens. Nikon has a service center in many countries. If you have one in your country then they can order the part. I have ordered from Nikon. They find the part number if you tell them your model and can email you an order form. Alternately Binoculars.com is very good to deal with as is Adorama Camera in New York. Both will sell internationally.