I see. The MM number is the aircraft serial.
Actually the red "1" you may make yourself. Just paint some of the clear decal background or part of the decsal sheet with the red. On the another side pencil the "1" digit of the correct size. The drawing has to be reversed if you want to get the correct red digit. And then just cut it out.
However there is the another qay ...
1. cut out the main squadron numbers. Do it as marked with the red. In the way you may limit the clear decal background reducing the possibility of the silvering additionally.
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2. Having that done cut out both of the "1" and then paint them red. Use slightly lighter red colour because of their "black background". When dried you may apply them on the model.
View attachment 745839