Here is a link to books on eBay that are about Brownies:
http://www.ebay.com/sch/i.html?_nkw=...at=0&_from=R40
The book by Sewell seems to be rare, but there is one on Amazon in the UK:
http://www.amazon.co.uk/Little-Brown.../dp/B002N989ZY
and a couple listed on eBay in the UK:
http://www.ebay.com/sch/i.html?_nkw=...=267&_from=R40