Three pointers,
first, put

use strict;
use warnings;
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at the top of your file. That would point out any jarring issue you have in your code (also surround your code here with <code></code> tags).
Declare your variables with my and run it again.

Two, say open(my $PARTS, '<', $partlist) and while (<$PARTS>) to better arrange your file handling.

Third, 0 is Perl's false state (among others) so unless ($found) would do (also, numeric equal is ==, not eq so you need to say $found == 0 and $PARTS eq $ordnum).

Try these and see what errors you pick up.

As for your code itself, you run through the entire @parts, then check on the state of $found. If $found is a counter (as you say in the comments, say $found++. If its an indicator, you need to do something when you locate a file.