Flash is a known issue, but my understanding is Adobe stopped Flash support for all android devices, so it's not just a Nook thing.
You could try using
BN's Flash plugin, this worked for me for most content.
Before you add the plugin, login to BN.com to edit your BN account info to a USA address, if it isn't already. Unfortunately, you'll have to provide credit card info for this 'free' purchase.
Puffin browser in the play store (get the free version to try) also comes with a 2 week trial of whatever version of flash they use.