Oz,
You could build in a field to collect that data on the product edit.php template.
How to modify templates:
https://www.wcvendors.com/kb/changing-vendor-templates/
Here is an example of adding a field to the product-edit.php template. The first part of the code would go into the template the second part into the theme/child theme functions.php:
https://gist.github.com/fervous/ce8059e2144f05b813c5932fbd1d3c6d
