For the 12dB cable assembies, you need a 25 ohm resistor and a 16 ohm resistor. The 10dB assembly needs two 16 ohm resistors. Use all non-inductive 10 watt parts, and build them up in blocks of four. So each really uses a "resistor block" made using four 10 watt resistors.

For the 25 ohm resistor used in the 12dB assembly, we use two pairs of series connected resistors, one a 20 ohm and the other a 30. The series connection gives 50 ohms and two of those in parallel makes 25 ohms.

The 16 ohm block is easier, since it uses four of the same part, a 16 ohm resistor. Two in series, and the 32 ohms that is formed is then connected in parallel to another just like it to make 16 ohms.

There are photos of the cable assemblies here.