I guess that the difficult part is the source. Do you know any webpage or service where I can get the bond prices of, lets say, most important countries.
I know that it is possible to do this in Bloomberg. But could I display the data obtained from there in an Android app?
FRED contains ''45,000 economic time series from 41 sources'', including bonds from several countries. Most likely the reported spreads are `end of period' (e.g. day, month, quarter, etc.) values, not tradable quotes. If you are looking for real time, tradable quotes, you'll be hard pressed to find free and redistributable data.