Buying an HOA lien in Colorado

Newbie here looking for some direction... I've found a foreclosed & vacant house in the Denver area that has a large outstanding HOA balance (most likely over 6 months of outstanding dues). The HOA hasn't filed a lien yet, but if they do would I be able to buy the lien privately or must the lien go to a sheriff's auction by law? The bank doesn't seem to know that it owns this property or else it would have sold the property after they foreclosed 6+ months ago. I'm sure I will have follow on questions to your answers so thank you in advance for your time and responses.