Get custom attribute text via MySQL

[LiamMcArthur]

I'm currently writing a PHP script (outside of my Magento 2 installation) that I will run on cron. This script sends orders to a supplier in a JSON format. I've managed to get most of the data I need but I'm struggling to get my custom attribute values of "size" and "colour". Does anybody know exactly which tables and ID's link to each other so that I can get the data? I've been trying to work it out for hours and I'm really struggling!

I hate to have to write a dirty script to do it this way, but I have no idea how to use the API to do this request and following the docs didn't really make it any clearer for me.

Thanks!

[Dmitry_Fedyuk]

I recommend to implement it as a Magento 2 extension, which is executed by Cron.

[LiamMcArthur]

I've looked but I can't find any 

[Dmitry_Fedyuk]

How can a Magento 2 extension schedule a cron job with a crontab.xml file: https://mage2.pro/t/576