Re: Malm Bed missing parts
Welcome to IKEAFANS, catalema.
The pieces you're missing are not sold separately, but come as part of the frame purchase and are packed in with the side rails. They are NOT specific to the Malm bed, so it's possible (but not likely) that you could find them from a secondary source.
You could make a pretty good imitation of them using a couple of 1x2's or 1x3's as a ledger board, which you'd screw into the sides of the bed using 1 1/4" screws. You need to be sure you install those pieces level both along the side of the bed and to the mid-beam.
When you try this, use the holes in the side rail as a guide - the top of your ledger board should be about 1/2" below the set of holes you'd be using for the long "L" bracket.
Because you're missing the metal rails, you won't be able to secure the slats to the rail using the plastic hardware bits supplied by IKEA. You can use some screws to this, though - screw through the top and bottom slats on each side into the ledger board. Because you're screwing so close to the end of the slats, make sure you drill a pilot hole through the end of the slats before you drive the screw, so you don't crack the slats with your screw.
Find out how you can get a piece of Chuck.
Just taking my inner IKEA geek out for a walk.