Can ya use EXS24 instruments, or just grab the samples out of them to use? I give a lot of stuff away in my day job and one of the things is, free EXS bass guitars. This is the big one- it has pre-roll on all the samples because I make the EXS24 player chop it off depending on velocity, so that soft notes lag a bit.
http://www.jinxtigr.com/f/ElectricBass.zip
Also got this one which I think is more straightforward, but it needs EXS24 even more 'cos it loops the notes, it's like a soundfont bass only with a sample for each note like the other one.
http://www.jinxtigr.com/f/FlatBass.zip