Does anyone know where to get a free testimonial slider for a right side bar? I found one but can get it to work.
There are lots of great sliders around, like bxSlider, but your description of what you need this for is a bit vague. If you can give more details, so can we. 
Just throw all your testimonials into a div and give that div a width and height and overflow auto. Prob not finding much because its so easy.
Depends what system you are working in.
Your question is to vague to give you a straight forward answer…
If you are using WP, use Testimonials Rotator… If not, look for JS slider like flexislider or flexslider.
Either search in google or check that one Testimonials Rotator might be requirement resolved.
Bx slider seems pretty good - is your web on WP or DW?