Jimmy,
I ran into this problem recently. The VDO sensor with the correct metric threads is just not available anywhere except Rotax dealers at a very large price.
However, there are several VDO sensors available from automotive suppliers that have threads that are a larger diameter than the M10x1.5 required to fit Rotax. A machine shop can easily machine off the threads of one of those and cut new M 10 x 1.5 threads. The one Matt identified is 1/8 NPT which is too small diameter to do this.
I found a good selection of VDO sensors at Summit Racing, a national mail order store. Just be sure to get a 300 deg F sensor.
Jim Butcher