is there a bus salzburg to bled, slovenia
Why would you want to do that by bus when there are good train connections? Austrian Rail shows an Austrian EC from Salzburg to Villach in 3h20m, a one hours stopover, and a 15 min train to Bled. The fare to Villach is about €31.
I did find a 22 hr, 6 change series of Postbuses to Villach taking about 22 hrs (with an evening to early morning stayover in a small town).
There might be some independent, long distance bus lines, but they don't show up on Austrian Rail.