two kinds of radio used on your model....
1) the Bavaria type; and,
2) the Commercial type.
i suppose you have the Bavaria type(by your description)... the flaps at teh side should show 2 holes-upper and lower.
u can fashion ur unlocking tool using coat hanger wire- shape it in a "U" so u can poke both holes simultaneously ( u'll need two of these- one for each side of the radio). push your "U" tool in and radio should come out