<?php
$re = '/<select name="ctl00\$ContentPlaceHolder1\$UrunListesi\$ctrl([0-9]{1,2})\$StokBoyut" id="ctl00_ContentPlaceHolder1_UrunListesi_ctrl([0-9]{1,2})_StokBoyut">([\s\S]*?)<\/select>/mi';
$str = '
<select name="ctl00$ContentPlaceHolder1$UrunListesi$ctrl0$StokBoyut" id="ctl00_ContentPlaceHolder1_UrunListesi_ctrl0_StokBoyut">
<option value="900061_50x80">50x80 Stok:0</option>
<option value="900067_60x110">60x110 Stok:0</option>
<option value="900037_70x140">70x140 Stok:0</option>
<option value="356593_80 T.Yolluk">80 T.Yolluk Stok:2</option>
<option value="356552_80x150">80x150 Stok:23</option>
</select>

<select>
<option value="dontwantthis">xxxx</option>
</select>

<select name="ctl00$ContentPlaceHolder1$UrunListesi$ctrl0$StokBoyut" id="ctl00_ContentPlaceHolder1_UrunListesi_ctrl0_StokBoyut">
<option value="900061_50x80">50x80 Stok:0</option>
<option value="900067_60x110">60x110 Stok:0</option>
<option value="900037_70x140">70x140 Stok:0</option>
<option value="356593_80 T.Yolluk">80 T.Yolluk Stok:2</option>
<option value="356552_80x150">80x150 Stok:23</option>
</select>

';

preg_match_all($re, $str, $matches);

foreach ($matches[0] as $select) {
    print "I like this select:______________\n";
    print $select . "\n";
    print "The values are:**********\n";
    preg_match_all('/value=".*?_(\d+(?:x\d+)?)[^"]*">.*?Stok:(\d+)/', $select, $values, PREG_SET_ORDER);
    foreach ($values as $value) {
        print "  - $value[1] and Stock=$value[2]\n";
    }
    print "\n\n";
}