How would I go about this?
upload suspicious file(s) to www.virustotal.com and test with 40+ malware scanners

alternatives: www.metascan-online.com / www.jotti.org

You can report and upload files to avast lab here: http://www.avast.com/contact-form.php
change subject on the form to suite your case

you can also use mail

send to virus@avast.com in a password protected zip file
mail subject: false positive or undetected sample (depends on your case)
zip password: infected

or you can send files from avast chest
how to use the chest. http://www.avast.com/faq.php?article=AVKB21