Have you tried powdering the bark yourself before extracting? What tek are you using?
Powdered bark is now considered "partially prepared" in the UK and therefore not easily bought online.
I get shredded bark in the UK and have had great results from an A/B extraction (similar to Marsofold's Tek). It isn't easy to get powder sent to the UK at the moment and shredded does work just as well if you powder it yourself.