I have never seen a Corsa shell for hobby-grade RC cars, so perhaps they were toy cars or special paintjobs on another type of shell that they were running. (Actually, there might be Corsa shells for the Mardave cars but they tend to be pretty unrealistic).
HPI used to make an Astra Coupe from the BTCC days. Tamiya made Cavalier/Vectra shells from the mid-90s BTCC/JTCC era. Protoform did the Astra and Vectra too. You might find them on eBay or in old shop stock.