is there a bus from bled, slovenia to dubrovnik, croatia
Bled is a small town and there wouldn't be direct bus service to Dubrovnik. You'd need to look at Ljubljana or Zagreb. There are buses from Zagreb to Dubrovnik, but it's a very long trip. You can check bus schedules within Croatia at www.akz.hr. Consider flying to Dubrovnik from Ljubljana or Zagreb. There are direct flights from both airports, and flying would save you possibly a half day (12 hours) of travel. The Ljubljana airport is actually half way between Bled and Ljubljana, so it's very convenient for your itinerary.
We were just in Dubrovnik last week. You can take a train from Ljubljana to Zagreb and then fly to Dubrovnik. It's super cheap, we paid 114 usd for 2 people. I don't know if this helps. Happy traveling.