what about the ability to send you a infected file ... or ...

[FetzBox22]

Is there any way to include something, (hidden from the non-experienced user), to send you possible infected files just using Malwarebytes?

or, 

maybe you could include a link to the forum with a sentence like "If you think, that there might be an infection on your computer that we missed, than follow these steps to send us your file".

And than you could lead them to a page where you tell them what you need (they need a forum account, and then a virustotal result and so on). 

Just to make it a little bit more easy accessible for any user to send you some possible infected file.