my @mos = ('01', '02', '03', '04', '05', '06', '07', '08', '09',
            10, 11, 12);
...
my @thirtyone = ('01', '02', '03', '04', '05', '06', '07', '08', '09',
            10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 
            23, 24, 25, 26, 27, 28, 29, 30, 31);
[download]

Leaving aside whether your approach is the right one, you could save yourself a lot of typing by learning about map and sprintf and by re-using what you have already built.

my @mos       = map { sprintf q{%02d}, $_ } 1 .. 12;
my @feb       = ( @mos, 13 .. 28 );
my @leap      = ( @feb, 29 );
my @thirty    = ( @leap, 30 );
my @thirtyone = ( @thirty, 31 );
[download]

I hope this is of interest.