Magento 1.7 – How to Get Requested Shipping Country in Cart Item Page

If you want to make it required no matter what, just hard-code it in the template. It should be on the input, not just the label.

<label for="postcode" class="required"><em>*</em><?php echo $this->__('Zip/Postal Code') ?></label>
   <div class="input-box">
      <input class="input-text validate-postcode required-entry" type="text" id="postcode" name="estimate_postcode" value="<?php echo $this->escapeHtml($this->getEstimatePostcode()) ?>" />
   </div>

You can:

1) copy file app\code\core\Mage\Checkout\Block\Cart\Shipping.php in the app\code\local\Mage\Checkout\Block\Cart\Shipping.php

2) define method

protected function _getQuote()
{
    return Mage::getSingleton('checkout/cart')->getQuote();
}

3) in the function getEstimateRates add

$this->_getQuote()->getShippingAddress()
        ->setCountryId($country)
        ->setCity($city)
        ->setPostcode($postcode)
        ->setRegionId($regionId)
        ->setRegion($region)
        ->setCollectShippingRates(true);
$this->_getQuote()->save();

where $country and other variables are you pre-defined values.

4) copy the template app\design\frontend\base\default\template\checkout\cart\shipping.phtml into your custom theme and adjust if if needed.