class YourCompany_YourModule_Block_Options extends Mage_Core_Block_Abstract
    {
    public function getStockMaximumQty()
    {
        $product = $this->getProduct();

        return $this->getProduct()->getStockItem()->getQty();
    }

    public function getProduct()
    {
        if(!$this->product){
            $this->product = Mage::registry('current_product');
        }
        return $this->product;
    }
}