If you're unsure a good place to start is sampling the colour with the dropper tool in Photoshop (Use something larger than a single point in Photoshop though, 5x5 would be best) , then click the foreground colour block (the colour you've sampled) and select the Pantone swatches pallette. Photoshop will then find the colour it thinks is closest.
Presumably you have a Pantone book? Tried just offering up the chips against a printed sample? Your eyes will be more accurate than anything else.
Not sure the legality of reproducing a company's logo without their permission though?