I managed to get my hands on the Thinkpad Tablet Keyboard Folio Case from Lenovo recently, fairly cheaply. I hadn't worried about one before as I found that
Lenovo’s ThinkPad Tablet is a good companion device for the more business-minded amongst us. Still, as with all tablets, it’s productivity quotient isn’t so high when it comes to on-screen typing. The FlexT9 keyboard is fine for basic text input, but when you write something longer than a few lines or want to type faster
If you don’t mind carrying the extra bulk, Lenovo's Keyboard Folio Case lives up to the ThinkPad brand’s reputation for having the best keyboards on the market.
Freestyle2
ORIOS Metal RGB
Eterno PG-5545
LX390
K65 RGB RAPIDFIRE Compact
G81-1800