98 Chevy Blazer gas tank valve

That flap comes with the tank. Im not aware of this being any problem at all. If its pushed in bending it damaged the flapper

The fill neck flap is part of the neck. Not hard to change out. Remove the cap, remove the two lines from the neck between the tank and the neck, take out the screws holding the neck to the body and remove the neck down and out. Reverse to install a replacement. Usually the flap only sticks if it's bent OR the spring fails.