The maths look a bit complex to me, but if you're running Mavericks or later, there's a simple workaround: you make an NSColor with the HSV/HSB values you have, and then retrieve the R, G and B values of the color:
use framework "Foundation"
on rgbFromH:hue saturation:sat value:val
set theColor to current application's NSColor's colorWithHue:hue / 360 saturation:sat / 100 brightness:val / 100 alpha:1.0
set theRed to theColor's redComponent()
set theGreen to theColor's greenComponent()
set theBlue to theColor's blueComponent()
return {(theRed * 255 + 0.5) div 1, (theGreen * 255 + 0.5) div 1, (theBlue * 255 + 0.5) div 1}
end rgbFromH:saturation:value:
its rgbFromH:0 saturation:57 value:85