At first i took an normal 100W/75mm halogen spotlight and remove the reflector and the socket.
Then i took an 8W LED modul from Seoul Semiconductor, which could be connected directly to 230V. I fixed it to an heatsink, using thermal compound. The wire has to be solderd on the module.
At least, i screw the heatsink into the housing, using the thread which was used for the original socket.
So the lamp has now only 8W instead of 100W, it don't get so hot anymore and the brightness is less then before but enough.
For more light, i think it is possible to assemble two modules.
a soldering iron
a little bit of wire
1 halogenspotlight 100W ( about 10€)
1 8W LED Module 230V ( about 10€)
a little bit thermal compound
2 screw long enough to fix the heatsink
Important: because this is a lamp with 230V you should be very careful. And don't forget to connect the earth