If you hold a National Collection you are required to allow visitors in to view your collection - under circumstances that fit the convenience of the collection-holder. When they were in Essex the MacLennans entertained a few groups each year but not, generally, individual visits. I imagine it will be the same now they are in Carlisle. So if you are in a club or society where the members might have an interest in snowdrops, see if you can persuade them to mount a group visit.