No Pur Bloka

Why is there a stock shortage of Pur Blocka again? When will it be available in pharmacies again? I've been taking propranolol for 12 years and have become reliant on it. I'm suffering without this medication and I'm wasting huge amounts of time going to the pharmacy and queuing over of over to be told there's no stock. Just typing this was a huge feat I'm shaking so badly. I can't just suddenly stop taking this medication. Should I ask my doctor for a different script? Please help.