In 1998 I organized an exhibition about Russell Page with the American Academy in Rome. On that occasion I reviewed his archive, which was then  kept in a very precarious and unofficial arrangement at the Kalmthout Arboretum, Belgium.
Russell Page left all his papers to the Family De Beldeers, who were personal friends of him; I do not know what the arrangements were at the time between M.me Helena De Beldeer, who legally owned the archive,  and the new management of the Arboretum; what I know is that I found the papers  kept in open boxes,  in a sort of a garage, without any proper archival device to preserve them against pests, humidity etc.
The person in charge  of the archive at the time was an architect,  Mr. Benoit Fondue, who claimed  that he had almost finished a catalogue raisonée of the archive, but  this catalogue actually never came out. However Mr. Fondue had made several lists of the papers, and I would suppose that since M.me De Beldeers has died   the collection  must have been  passed over to the Arboretum. I would think  he is still in charge; I hope   the drawings and other papers have not passed into private hands and have received the attention they deserve.
I suggested at the time that the whole bulk be passed to a serious archival institution that would give the documents the proper care, and a place  where researchers and scholars could have easier access and facility, but to no end.
I would suggest then that now   the person to contact is the general director of the Arboretum, and I am copying this message to their email address.

February 8 - Belgium Garden Writer to England -
Page was indeed not a prophet in his own country. As a homosexual, he had fallen out with his family and was an extremely solitary person. At the De Belders, he found a family who loved and understood him for his qualities, a garden where he could experiment freely and a tremendous source of energy and inspiration.
When studying in France , he was helped and encouraged by André de Vilmorin, a descendant of a remarkable family, devoted to plants for generations.
He had a good friend and admirer in Gabrielle Van Zuylen (lives in Paris ), who wrote a book about his gardens. The archives are sorted and kept in an attic in good conditions. I believe all his plans and sketches are there, except  things previous to WWII, which all burnt when the building they were kept in was bombed.  It must not be forgotten that R. Page had offered his archive to the RHS and the Victoria and Albert Museum , who turned down the offer! There had also been contacts, after his death, with Dumbarton Oaks, Washington D.C.
As to the place he was laid to rest, I quote a text on Page, written by Jelena De Belder, in my book : "The burial was simple and intimate. The Duke and Duchess of Beaufort offered a sheltered spot under an oak tree in their park, which he knew well."
It is always a pleasure to discuss remarkable people and ensure the interest in them remains alive.