Most of them, if not all, can also be found on youtube with descriptions, explanations and sometimes tutorials. The vst3 instruments listed in the link above are all free, there are other websites like this one, which are to be found with a 'free vst download' search. With the help of the MS4 manual, the administrators and all the other participants in the forum, you should be able to achieve that. Switch to MS4 for the vst3 support (MS3 doesn't), which on the long run is the best choice for the quality of the instruments, but is this support already functional ? I have no idea, i have never been a musescore user.
Keep on with MS3 and still try to find soundfonts (musicals artifacts, youtube) that will integrate well enough, or, I record music in real time in 'Energyxt' with vst2 instruments, and some soundfonts.
