Got mine at Land Rover Parts and Accessories from RovahFarm and it's an expensive little thing. Rebuilt mine 2 times, but 200k + at the time, it wobbled and the housing started cracking. So I got a new one. No problem since.
Mine started the cutting out about 50-55mph and it be okay. Sometimes I could drive a few hundred miles no problem. But it started getting worse as described in above post, even at a stop light taking off, I wanted to burn my truck at times.
If rovahfarms doesn't have it, Land Rover parts, spares, Land Rover accessories, all models - speedometer transducer more expensive here to.

Not sure if yours is the same as a 98 or not though. It's also called a Speedometer Transducer . My model no. YBE100540

Verify with one of the above poster.

GEMS models 96 - 99 1/2 are roughly the same throughout except when it comes to the Evap system (can, fuel pump and purge valve) and window hardware.