Hi all, since I really like the idea of Wouter, but don't want to burden him with all the work of creating icons for every used I whipped up a small application that will generate these images on the fly. You can use basically any FontAwesome icon :)
You can check it out here: https://github.com/bluewalk/FontAwesomeToBunqAvatar/ and download here: https://github.com/bluewalk/FontAwesomeToBunqAvatar/releases/download/v1.0/FontAwesomeToBunqAvatar_v1.0.zip
*Note, this is just a first version. I will be adding the colours of bunq and future fixes if required.