Java 8, 105 bytes

A void lambda accepting a mutable java.util.Set<String>.

s->{for(int i=0,a,b;i<49;)if(s.add(""+(a=i/7)+(b=i++%7))&(s.add(""+b+a)|a==b))System.out.print(" "+a+b);}

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Ungolfed

s -> {
    for (int i = 0, a, b; i < 49;)
        if (
            s.add("" + (a = i / 7) + (b = i++ % 7))
            & (
                s.add("" + b + a)
                | a == b
            )
        )
            System.out.print(" " + a + b);
}

Acknowledgments

• -1 byte thanks to Jonathan Frech