You would have to write ahead to arrange it but the finest private collection of conifers I have seen in the UK is in the garden of Alan and Adrian Bloom, owners of Blooms of Bressingham perennial nursery in the moorlands northeast of London. I was taken through the garden by one of the Horticulturists at the perennial nursery that I contacted ahead of time. You will want to devote the better part of a day if you go there as the perennial nursery has a wonder display garden, in addition to the Bloom's private conifer garden. It is well worth the effort before hand to arrange a visit.