Aaarrgghh, I managed to run down a copy of Vol 2 Part I in the Petrucci database, but that tune's not in it, so it must be in Vol 2 Part Something Else. That volume's page 71 boasts a tune that rejoices in the name of Tuzzy Muzzy, and there's no Lewis Castle listed in the table of contents.

This crowd (below) seems to have Books II and IV in their collection, though you'll have to write them because I couldn't see a download, only a mention:

http://sites.scran.ac.uk/jmhenderson/web/collection/jmhcoll/walsh.htm

(Please excuse the lack of a clickable link - Mudcat is slower than frozen molasses today and it was taking ages so I bailed out.) Their contact info is:

The North East Folklore Archive
Henderson Collection
Aden Country Park
Mintlaw
Aberdeenshire AB42 5FQ
Scotland UK

E-Mail: nefa@enterprise.net
Telephone: +44 (0) 1771 623938
Fax: +44 (0) 1771 623937

You could also get in touch with the infinitely-helpful National Library of Scotland.

Does it have to be from that historical source? Otherwise I assume you've tried the online tune sites like www.thesession.org etc?

Let us know if (& where) you find it, especially if it's downloadable.