Hi there, mattrobbs-yahoo-.
Currently, the ability to connect the Amazon Business app to your QuickBooks Online UK account is not available. This may be the reason why you're unable to search it.
Though you may try look any other particular 3rd party app that integrate with QuickBooks. We can not recommend any in particular as we do not make the apps but welcome any feedback from other Community users if they are using an app which they want to recommend.
Keep me posted if you have any other questions with this concern. I'll make sure to get back to you as soon as I can. Enjoy your weekday and stay safe!