G'day, and welcome to the forum! Airfix have rereleased that kit, so you should be able to find it on the 'Hannants' (UK) or 'Squadron' (US) hobby shop websites, among others. If still no joy, drop me a PM!
By the way, Italeri either have, or are going to, release a new Sunderland Mk.I kit too, quite different to the Mk.III version that Airfix produce. Do you know what squadron your boyfriend's father was in? It might help clarify the version used, and which kit would be better.
Boats... don't know how I missed this thread, but nice work on indeed on (IMO too) the most beautiful of the 'boats... One question though, how come the streaks down the fuse' and across the wings?