Woocommerce product variations, Google product feed and nested loops in WordPress

I’m trying to make a Google product feed from Woocommerce – the available plugins to do this don’t support product variations, which is a bit of a nuisance.

I’m working on a clothing shop with multiple sizes and colours of item, so it’s required that the Google product feed should list all available size/colour combinations, and as it’s doing stock control for each variation, there is no point listing the Size 10 White as in stock when all we really have left is Size 14 Brown.

So, I reckon what I need to do is create a product feed that runs a loop for each product, then inside that loop, runs a nested loop for each variation? It’s a bit slow, so please suggest a better way if there is one! At least it will only have to run once a month.

Here’s what I have so far:

 <?php
// First get the main product details.  
$args = array( 'post_type' => 'product', 'posts_per_page' => 999 );
$loop = new WP_Query( $args );
while ( $loop->have_posts() ) : $loop->the_post(); global $product;

// Now do a second nested loop to get the variations. 
$args2 = array( 'post_type' => 'product_variation', 'post_parent' =>'$id');
$variationloop = new WP_Query( $args2 );
while ( $variationloop->have_posts() ) : $variationloop->the_post();

// get the parent of each variation so we can use $parent (is this necessary???)
$parent = get_post($post->post_parent); 
?>

I feel that really having done the first loop, I should be able to call things from that, but once the second, variation loop is done, I don’t seem to be able to refer to anything within the first, product loop. Hence get_post($post->post_parent)

And then I do the feed. So far this seems to work:

    <item>
    <title><?php   echo $parent->post_title;?></title>
    <link>http://mysite.com/shop/<?php   echo $parent->post_name;?></link>
    <g:image_link><?php echo wp_get_attachment_url( get_post_thumbnail_id() ) ?></g:image_link>
    <g:price><?php echo $product->price ?></g:price>
    <g:condition>New</g:condition>
    <g:id><?php echo $id; ?></g:id>  
    <g:availability><?php echo $product->is_in_stock() ? get_option('product_in_stock') : get_option('product_out_stock'); ?></g:availability>
    <g:brand>My Brandname</g:brand>
    <g:product_type>Clothing &amp; Accessories &gt;  Clothing &gt;  Swimwear</g:product_type>
    <g:google_product_category>Clothing &amp; Accessories &gt;  Clothing &gt;  Swimwear</g:google_product_category>
    <g:shipping_weight><?php echo $product->get_weight();?></g:shipping_weight>

    <g:mpn><?php echo $product->get_sku(); ?></g:mpn>
    <?php if (get_option('rss_use_excerpt')) : ?>
    <description><![CDATA[<?php echo $parent->post_excerpt; ?>]]></description>
    <?php else : ?>
    <description><![CDATA[<?php echo $parent->post_excerpt; ?>]]></description>

    <?php endif; ?>

Only this is incomplete – I’m not sure how to get at all the elements that I need. In particular, how do I retrieve the variation size and colour, which are in a different table?