Some websites post instructions for C-frame bunk beds. The sites that sell these unique beds will be the most likely to carry them, so look there first. Ask the previous owner of the bunk bed where they bought theirs and then visit that store's online shop. Or, visit them in person; often a set of instructions is just a phone call away. If you are unable to locate a hard copy, try to put the bed together yourself by following a general rule of assembly.
Assembling a C-frame bunk bed starts with the two large side pieces. Most beds have one-piece sides which are connected to the horizontal bed frame pieces. Locate these two side pieces and place them flat against a wall. Have a helper hold them upright and then place the cross beams in between them to start to form a visual of the bed. Remember that the bunk bed frame on top will not include the futon assembly. Place this frame, along with its hardware, in a separate area than the top bunk frame as they may have similar parts and are confused easily.
Once you have the major parts separated locate the hardware and separate the screws by length and size. Place them each in a pile and, using the process of elimination, figure out where each one goes. Count the number of screws included and match them to the number of mounting holes in the various brackets and frame pieces. Larger screws are used to attach the frame pieces, smaller screws for mounting brackets and the lower futon frame with its spring loaded arm. Attach this part to the "C" frame sides, and then attach the top bunk bed frame pieces into the slots on the sides. The longer bolts are used to attach the front and back top bed rails.