You could try something like this:

my %numbered;
foreach my $string (@a) {
    for ($string =~ /(\d+)/g) {
        push @{$numbered{$_}}, $string;
    }
}
my @occurances;
for (@b) {
    push @occurances, @{$numbered{$_}} if exists $numbered{$_};
}
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Rough code, untested. Your data may allow some simplification.

After Compline,
Zaxo