Originally Posted By: cubalibre
...can I use them with sforzando?
what extension have the samples libraries? wav?

Yes you can use them with Sforzando VSTi, just google free SFZ.
They are usually wav.
SF2 is the old SoundFont format, the GM ones have a library of instruments within them.
The single instrument SF2 format can't have articulations in the instrument like a keyswitch for slide, vibrato, bend, HO, PO etc, but the SFZ can.

There are lots of single SFZ instruments here UserTracks (and other add-ons)
as well as ones with a large instrument library like Virtual Playing Orchestra & No Budget Band - Guitar - Bass - Organ - Synth - Orchestral

You can get Native Instruments Kontakt vsti/standalone they have sales around Black Friday, that comes with an instrument library and you can also buy 3rd party instruments for it.
Here's one company with good value instruments for Kontakt http://www.indiginus.com/