This might help:

http://home.cogeco.ca/~sapphire/

Hmmm... i guess the description of the sensor isn't very clear.

When you buy an alfa, it come with basically the same style of sensor (different housing i think).  

The Alfa sensor (and the one from sapphire electronics) work by detecting a magnet that passes by.... say magnets that were attached to a driveshaft.

Your not gonna find something that will bolt directly to your transmission, because everyone has a different application... some people mount to the tranny, some mount to the rear disc/drum, some mount to the rim... it's completely up to your imagination (and fab skills) to come up with a suitable mounting location.

On my VW Fox, I bent a piece of flat steel into an L... the long side bolts through a hole in the transmission housing, and the hall effect sensor mounts to a hole drilled in the short end of the L... then the magnets(very strong.... watch your fingers!) were glued to the driveshaft to prevent slippage.  Because of the housing on the sensor, it's distance relative to the magnets could be adjusted (entire housing is threaded, and two nuts hold it to the bracket.

Now, if you went somewhere that specializes in rally cars (Four star motorsports comes to mind), they may be willing to fab up something for you... for a price.

BTW.... sapphire electronics is located in the peterborough ontario area.... try sending them an email... they might be able to send you a picture of what the sensor looks like.