You might be able to install a hood from a *similar* year Camaro (perhaps a 1990-1992 model), but even then, you should expect some potential fitment issues that may require adjustments. Aftermarket hoods (performance hoods, etc.) are designed to fit a specific year and model, but these are also usually made to look different.
Before buying any hood, you should verify its compatibility with your specific 1991 Camaro model (IROC-Z, RS, etc.). Checking with parts suppliers or online forums dedicated to third-generation Camaros is highly recommended.