2 items please use the drop down menu for each one 
 
5mm WHITE acrylic replacement cover (Please let me know if this is going to be ok, as you mentioned your original piece being 13mm thick) (We only have 3mm or 5mm) 
This will have the notches as per images sent
Overall dimensions 340mm x 380mm with 12mm 'notch' protruding out twice at each end (shorter side) 
 
 
BLACK MDF 6mm thick rectangle 395 x 590 (slightly rounded corners)