Truck bed not level

Greetings, I own a 2017 Tacoma with 5-1/2 bed. The bed had been replaced after the original had been damaged. The problem is that bed is lower in the front than the rear. This became evident when I installed a camper shell, giving the vehicle a noticeable v shape where the bed meets the cab. Obviously, spacers were not installed in the front when the bed was replaced. I need advice as to where I can find the correct front box spacers/insulators for this vehicle or if I can improvise with some other material or devices. Also need some advice on installation to remedy the height difference without removing the bed entirely.