Have you tried contacting the Fiji Museum?
They have posted photos on their Facebook page (
https://www.facebook.com/fijimuseum) from WWII - the Bilo Gun Site near Suva. I'm sure they'll have information for the site in Buca.
Their email address as listed on their website is
fijimuseum@kidanet.net.fj or you can make a quiry online
http://www.fijimuseum.org.fj/contact_generalenquiry.htmlRegards,
Dulcie