Group Pricing + available products

I have a group pricing setup - I'll call it Group1.

I would like to make 1 of the products available ONLY to those people in Group1

Is this possible & if so, how do I do it?

You would need something to either flag this product or hard code the products_id where the buttons are generated to manage this ...

All of the button calls are passed through a function to manage when they show as links, buttons, turned off etc. in the:
/includes/functions/functions_general.php

using the function zen_get_buy_now_button to handle this:

////
// Switch buy now button based on call for price sold out etc.
  function zen_get_buy_now_button($product_id, $link, $additional_link = false) {
    global $db;

You could force a lookup or something for various reasons to determin when and what displays on various products ...