You already had the NMB (Thai) keyboard which is widely regarded to as being the best. You should replace your old keyboard with exactly the same one.
Call IBM and honestly explain your problem. You never know, but they might just send you another one. If not, the keyboards aren't that expensive, so you should be able to buy one yourself.
I've had success buying missing keys for my thinkpads from ebay in the past, I'm having a little trouble though finding missing keys for my thinkpad...