You could split into pairs on a '<' or a '>' optionally followed by ':<' then split the pairs on a comma.

johngg@shiraz:~/perl/Monks > perl -Mstrict -Mwarnings -E '
my $str = q{<1,2>:<5,7>:<3,0>};
my @nos = map { split m{,} } split m{(?x) < | > (?: :< )?}, $str;
say for @nos;'
1
2
5
7
3
0
[download]

I hope this is helpful.

Update: Changed quantifier from * to ?.