Hello I am having a hard time finding a mesh screen for my 80 gallon aquarium

[Xhero]

I have a 80 gallon aquarium that I want to turn into a reptile enclosure. I went to petsmart and they only sell 50 gallon screen mesh lids . Does anyone know where I can get a proper lid for my tank that fits right . The glass canopy is 48x18 but the glass has a gap. So I'm not sure exactly what size lid I need. ...Plz take a look at the pictures of the aquarium and the measurement.. not sure if I did the measurements right ether plz help( please excuses the dirty tank I still need to clean it up and remove the rest of the sand)