If the shares were a gift or inheritance, then the value would have been the value (number of shares x price ) at the time. The company secretary should be able to give information on the share price.
You will have to try and get a record of shares splits, bonus issues, etc to arrive at the number of shares that were sold for € 10,000
The initial cost can be indexed up to take account of inflation.
If a broker held the shares, then they should have historic information.