Shopify Liquid - With this Liquid snippet, you are able to grab variants of a product, assign it to an option within a Select HTML element. This also grabs the product sku number, variant value, title, and variant URL. Currently set to 3, but can be extended for however many you need.

product-get-specific-product.liquid

{% comment %}Assign products set in Settings to variables{% endcomment %}
{% assign productOne = all_products[settings.product_one] %}
{% assign productTwo = all_products[settings.product_two] %}
{% assign productThree = all_products[settings.product_three] %}

<!--Output variant info to option elements within a Select HTML element-->
  <select>
    {%for variant in productOne.variants%}
      <option sku="{{variant.sku}}" value="{{variant.url | split: '?variant=' | last}}">1 - {{variant.title}} - {{productOne.url}}</option>
    {%endfor%}
    {%for variant in productTwo.variants%}
      <option sku="{{variant.sku}}" value="{{variant.url | split: '?variant=' | last}}">2 - {{variant.title}} - {{productTwo.url}}</option>
    {%endfor%}
    {%for variant in productThree.variants%}
      <option sku="{{variant.sku}}" value="{{variant.url | split: '?variant=' | last}}">3 - {{variant.title}} - {{productThree.url}}</option>
    {%endfor%}
  </select>