The address is: Noordwal 521, 2513 DX, Scheveningen. The telephone book does not give any Gysen on this address, but you could write a letter, maybe the present tenant or owner knows more. I could find only one Gysen in Den Haag (Scheveningen is part of Den Haag): W.P. Gysen, Tennisbaan 8, 2492 WP, Den Haag. Maybe they can help you.