I broke one of the slat boards in my kid's Mydal bunk bed from IKEA.
I believe I can get smth similar enough from ACE hardware (and cut it to size, and drill holes) - but on the off chance someone already has boards lying around...
Length: a tad over 38"
Width: 2.5" or more
Twin bed slat (20008, near Van Ness metrostop)