There are MANY types of rubber spoilers available whether OE for certain trims, or mass-customized to suit certain makes. This has been a trend esp for boxy-shaped cars.
Construction wise, there are as many fibers as originals as well. Fibers that wanting to "look" and "shaped" like the original rubber spoiler counterparts.
BMW E30 series - small and big, SAAB, Honda's CA, Lancer A174 and tons more.
For which specific car model you want this for?