while(<SOURCE>) {
    my $source = $_;
    #skip blank lines
    next if ($source =~ m/^(\s)*$/);
    if (substr($source,145,16) =~ /Page:          1/) {
        $page1 = 1;
        next;
    }
    if (substr($source,76,11) =~ /Run Listing/) {
        $reporttype = 1;
        next;
    }
    if (substr($source,72,9) =~ /Sorter: 2/) {
        $sorter2 = 1;
        if ($page1 == 1 and $reporttype == 1 and $sorter2 == 1){   
        ++$dcount;
        print substr($source,83,20) . "\n";
        $page1 = 0;
        $reporttype = 0;
        $sorter2 = 0;
        next;
        }
    }
[download]

You could consider the following things:

• Don't use $_ as loop variable; use $source directly
• remove the parentheses in the regex (for skipping blank lines); you don't need to capture the whitespaces, do you?
• compare fixed strings directly (without regex); check Equality Operators for info about eq and ne
• I don't see a need for $sorter2; just leave it out.
• If all your ifs are alternatives, you can use if/elsif/elsif(/else) and leave out the next calls.

So this is, what I came up with:

# don't bother $_; use $source directly as loop variable
while ( my $source = <SOURCE> ) {

    # skip blank lines; no need for capturing ()
    next if $source =~ m/^\s*$/;

    # compare fixed strings directly without regex; use operators eq o
+r ne 
    if ( substr( $source, 145, 16 ) eq 'Page:          1' ) {
        $page1 = 1;
    }
    elsif ( substr( $source, 76, 11 ) eq 'Run Listing' ) {
        $reporttype = 1;
    }
    elsif ( substr( $source, 72, 9 ) eq 'Sorter: 2' ) {

        # no need for $sorter2; just check the other variables and do 
+your stuff 
        if ( $page1 == 1 and $reporttype == 1 ) {
            # just personal preference; post increment
            $dcount++;

            # personal preference; print a list instead of concatted s
+trings
            print substr( $source, 83, 20 ), "\n";

            $page1 = 0;
            $reporttype = 0;
            
            # leave out next, if there is no more code in the while-lo
+op
            #next;
        }
    }

    # no other stuff here?
}
[download]