Hasbro, Wizards of the Coast's owners, are slowly reissuing much of the rpg tie-in fiction "back-list" and making good the ravages made into the catalogue over the "interesting times" seen over the past few years - the damage done to it by themselves, and WotC before them, once they'd bought the wreck of TSR, but not those set in the Birthright Setting (nor those set in the Alternity StarDrive, Darkspace, Greyhawk, Ravenloft and Spelljammer worlds).
The Birthright novels are therefore liable to become increasingly difficult to find, as time goes on.
I list here both what I have in stock, and what I may be able to restock, or find second-hand; n.b. all of these books are now out of print. If a title you are hunting is not listed as in stock here, i may still be able to find a copy of it for you: e-mail me at v$imt$v at my sub-domain, i-m-t.demon.co.uk to ask.
Please use the same e-mail address to enquire about postage costs, and to order.
(e-address spelled out to reduce/avoid unfriendly e-address harvesting)