I am not sure where to get this done but if your vehicle is worth more than the book value and you want to insure your vehicle for the larger amount, get an apprasial.
Usually an insurance will insure the vehicle for the increased amount if you want to pay for it.
Have you had any bad dealings with this company ?
Is insurance company an Agency or the actual Insurance Company ?
Call the Insurance Company and ask for information, if it is what you want, present it to your Agent.
Sometimes Insurance Companies will increase the amount if you agree to specific qualification to the pay out. i.e. if the vehicle is stolen there is a pay out. If there is body damage theat happened in the woods (try an prove it) or by abuse then there is no pay out.
My Home Owners policy had no problem nicrease the rider to cover my wife's diamond ring. I guess it all depends on what they consider the risk to be.
There are Antique Car Insurance Companies too.