I got a china knock-off diffuser that is made of fragile PP plastic so once slight touch with anything was enough to break off 3 clips and one fixing point.
It was DIY! time...
1 - jack up the car, fix it properly, place a stand to avoid fall down related recovery period
2 - dig the garbage to find a carton/paper box sheet
4 - do some basic measurements, cut a rough shape a try it on
5 - ask why point 3 is missing and start looking for scissors and sharp/tool knife
6 - re-do the shaping to a fresh muck up as your 1st attempt will be off for sure
7 - transfer it to plywood, alu sheet, ABS plastic or whatever you desire to fabricate it from
8 - ad same rakes/fences to guide the air and to reinforce it (remember, idea is to have the air attached as long as possible, make it gap-less fit to a plastic end part of diffuser, fences should be going from small to tall and narrow to wide, air behind the wheels should be excluded as it is to turbulent anyway)
9 - paint it black, make sure it does not touch the exhaust pipes or does not melt if made out of plastic/fiber
10 - go for a drive and enjoy the feeling how it sucks panties under your car along your drive path
PS - I am aware that is way too small to create any downforce, its main purpose it to secure the diffuser and to cover those giant holes in between differential, exhaust and bumper...