The Girling information I found for 106 Series 2 cars (2600 cars with disc brakes all around) indicates that the front rotors are Girling type "17/3P disc" and the rear rotors are listed as type "12/10/3 disc" with "8 x 1-1/4 GNSM" hand brake.
Girling literature lists the same type of front rotor for AC 428 (1970 only), Aston Martin DB6 (1966-69), Austin 3 Litre (1968 onward), Daimler Sovereign, Jaguar 420 (1966-68), Jaguar XJ6 (all models), Jensen Interceptor and FF, Scimitar GTE, and Rover 3500 (P6B) Mk. I-II to and 'S' models. Of those, I find Austin Healey 3000 most promising. Moss Motors lists 2 types of rotors for these cars, of which the later version (from chassis 26705 onward) might be the one referred to in the Girling literature. These rotors with Mosso Motors part no. "021-201" are listed at only about $45 a piece -- well worth looking into, I believe (disks that fit out cars may need some holes drilled in the correct positions).
AlfaStop in the UK has rear rotors listed as "Regular Stock" on their web site. For the rear rotors, I found only a derivative in the Girling literature, namely the "12/10/3H disc" for the Lamborghini Espada, and I would expect mentioning that name to a dealer quickly translates to a huge price tag.