I've bought the prosonus strings .gig from bigfishaudio.com, it costs 50 dollars (IIRC) and provides 5 .gig files:
String section
Double-Bass
Cello
Viola
Violin

Each if the files has about 8 different dynamics, pizzi, tremolo, marcato, and more, and are all multi-layer sampled.

They all load in linuxsampler, just make sure your getting the .gig gigasampler version! (There's also a kontact lib or something).

If you want sound samples, there are some on the page on bigfishaudio, and some on my SoundCloud: can link if you wish.

Hth, -Harry