Do U know the basicis of fiber glass? If so u can make your own air dam.
I use great stuff expanding foam on the part of bumper you want to change. Spray it on and let it do its thing. Then use a kinfe or saw to cut the foam into a close shape. then use 40 or 80 grit sandpaper to final shape it.
Once the shape is how u want it then u tape aluminum foil over it to protect it from the fiber resin go larger than you will need. If the resin gets on the foam it will melt it.
After this use Matt or flece and resin to lay over the foil let it harden. Again go bigger than u will need.
Once it hardens you can pop off the mold and trim it to fit your bumper. Then cut off the bumper and foam and atach yours with rivets then mold it to the bumper using more matt and resin layering the part to make it stiff as the original.
Then sand and finnish.
All in all it will take some work. And this is only if u want to stay fiber glass. U could make it out of metal and just riveit it to the bumper.
