Try these http://www.sgs-engineering.com I've had replacements from them in the past (not on my X but they can cross reference OEM part nos). Their re-gassing service is spot on too. Send your old ones in, they will check them and if they are suitable they will re-gass the and even uprate them ...

First couple of cold days of the winter I got the warning gong and message in HUD. Its stopped working now. Temp still shows ok when cycling through BC.