Hi,
There should already be a second instance.
If I search for that text in the code of the default show_block_address view file, I can find both:
<button onclick="return window.checkout.newAddress(<?php echo $this->step; ?>,<?php echo $this->module_position; ?>, 'billing');" class="<?php echo $this->config->get('css_button','hikabtn'); ?> hikashop_checkout_address_new_button"><?php echo JText::_('HIKA_NEW'); ?></button>
and:
<button onclick="return window.checkout.newAddress(<?php echo $this->step; ?>,<?php echo $this->module_position; ?>, 'shipping');" class="<?php echo $this->config->get('css_button','hikabtn'); ?> hikashop_checkout_address_new_button"><?php echo JText::_('HIKA_NEW'); ?></button>
One for billing and one for shipping.
I don't see why you would get only one of them in that file if you get the two buttons unless you did some wild modifications in that view file.