Well as far as I know the Secret Service were never issued the Model 58, but I could be wrong.

I believe there is only 1 known gold and blue pinto that is factory original. I am also fairly confident that they wouldnt have gold plated the hammer, trigger, or ejector rod.

Without seeing pictures I believe it is refinished and should be valued as such. Any N frame in good shootable condition is worth right around $500 in my book. That's where I would start.