A McKelvey family tree exists in the Blackwood Family History manuscript trees Collection in the LinenHall library, Belfast. My advice is visit yourself if possible, giving them time to have the volumes available, however as is more likely you may live abroad I suggest you ask them for photocopying estimates if they think your knowledge relevant and be prepared to pay the extra for post and packing if you are tempted. “The Library welcomes all research enquiries, whether made in person, by phone, fax, letter or e-mail. Enquiries from members will be answered free of charge. Visitors from afar, and in particular those engaged in serious research projects, are recommended to make prior contact with the Library to ensure that they receive the best possible service. More complex enquiries should be made by letter, fax, or e-mail. Enquiries of this kind from within the British Isles will normally be answered free of charge, apart from any copying and postage charges. A minimum charge of £2 will normally be made in respect of overseas enquiries. A4 photocopies b&w are 20p. The Library may be able to assist those with more extensive research requirements on terms subject to negotiation with the Librarian. Contact the Library for further information on email@example.com
or Telephone 028 9032 1707. Their address is The Linen Hall Library,17 Donegall Square North, Belfast BT15GB, Northern Ireland, see their website for contact details or use Email:firstname.lastname@example.org
The volume references are
Hoping this is includes new information for you
good luck, Jim
ps However if the material is really relevant when you get it, I suggest a further donation to this unique library that is always needing extra funds.
Have you tried NIFHS genealogical index in resources