Did a search on the Web "Bosch fuel injectors 0 280 150 105" and came up with all sorts of interesting stuff.
They are 1975 Manta injectors and also OEM for Rover Vitesse; Alfa 2.5L & 3.0L; Jaguar XJS; Porche; Renault & Triumph so I guess they are still available new.
Try
www.boschusa.com also try a search for "0 280 150 105" on this buliten board
www.opelgt.com