The Royal Naval Philatelic Society are also issuing covers, the design bearing three illustrations of Nelson at various ages, plus a view of the Rectory:
http://www.rnphilatelic.org/rnps/
Click on 'covers', view cover list, then Series 8 to view.
They are due to come out in October and consist of a limited edition of 410, signed and unsigned. The various signed will be autographed by members of the Clergy and connected to churches with Nelsonian connections, eg Burnham Thorpe, as well as by Anna Tribe (Nelson's G-G-G grand Daughter) and Mary Arthur (Nelson's G-G-G-G Grand Daughter.)
They also of course have other covers, although not all may be available.
Kester.