Hi I am living in Peninsular Malaysia (Kuala Lumpur actually) and I have 3 Reiger Begonias. If I can help you with anything, let me know. Personally I haven't read or seen the book you mentioned but hey, since I'm in that part of the world..perhaps I can help out.

Thanks for your reply Eileen. We have tuberous,cane,and rex begonias but don't have any Reiger begonias, but they are sold in the uk in shops as winter flowering plants.
We have copied the website address for the book so you can have a look yourself :-
http://www.nhpborneo.com/onlinestore/product_details.asp?id=859
If you do see it somewhere and you think it looks good for the money please could you let us know. Thank you

The books is available in the UK from NHBS Books (link below).

Here is a link that might be useful: NHBS

Shipping from npborneo directly is still very expensive.
Lucklily there is another dealer who is nearer to the UK:
https://www.koeltz.com/indexSecure.cfm?pg=%2FBotany%2Ecfm%3FUserName%3D%26CurrentCat%3D80113%26CurrentType%3DNew%26Page%3D5

Here is a link that might be useful: Koeltz Scientific Books, Germany