Sounds like it is for insurance purposes, do you have 'agreed value' policies in Europe? They are common over here, you agree the value you are insuring the car for and pay the premium accordingly, then if anything happens that is the amount you get. As long as your declared value is within the range of actual sales then the insurance company doesn't usually require an independent appraisal.
If it is abnormally high they might, in my case I presented he few documented sales I could find of true GT5 cars and they allowed me to insure similarly.
It depends if you need the appraisal from a licensed appraiser or just from someone knowledgeable? You could also try presenting the data Hagerty has on their valuation tool, which is derived from a cross section of recent sales.