Welcome to Just Answer. I will do my best to fully answer your question(s).
A local plumbing supplier or contractor can order specific pipe clamps in the sizes (likely 1 1/2") that are a chrome type finish that can secure the risers (1/2" ?) then the drain with a chrome rod that can be cut to exact required length. the rod is then fastened to the pipe clamp with a hidden set screw. Sorry I do not recall the exact name of these types of clamps but I have purchased them once long ago for a job I once did. It looked very nice when finished. Best to see if a plumbing place can order them. I highly doubt you would have any luck at a home depot and such. But I would write them off either. They may have the same clamps in a non- finish like black iron pipe though.
The risers come with parts something similar to your answer. However, the fastening rod and support has a screw at the end that is supposed to be drilled into the tub, If the tub is cast iron or volcanic stone, then the screw connection is useless. I would like you to provide the name of the pipe clamp you are referring to. There are two risers (hot/cold) 3/4 that need to be secured external overflow drain (1 1/2).
Here is a clamp similar to what I am refering to:
Looking at google images there are a few different designs that would work for your needs. You get one size for the riser (total of 2- 3/4" and 2 that are 1 1/2") use the rod in between to secure it all together.
ok, I see that it may work. I wonder if there is a formal name for it other than chrome pipe clamp?
Each manufacture has it own name for their specific clamp. I call them a metal "full wrap" pipe clamp. Some call them a clevis hanger clamp.
Another thing I saw was pipe holders, one for each riser, screwed into the wall. That might work too. Thanks for your help