Your best bet for some of the larger parts is the marketplace on this site or ebay. I had a hard enough time finding a "complete" internal rebuild kit for my carbs.
Most rebuild kits only have the basic internal parts; float bowl gaskets, float needles, float needle "seat" and maybe an o-ring or washer.
To get the rest of the parts in a single kit; the idle mixture screws/springs, emulsion needles, emulsion tube, etc I had to order a Keyster kit out of
Canada and they sell them out
constantly. Using the part number for this kit I was only ever able to find another company in Germany and I think the UK that sold the same one.
I have an older '78 SOHC, so I am not sure what the difference is betweem our carbs (yours is an '81 sohc?) in regard to emulsion tubes, emulsion needles, float valves, etc. These kits might not work for you since they are labeled for older bikes, but there may be a similar one available somewhere.
Now, the enrichment rod and the associated plungers/valves are a whole different story. You may only be able to get replacement parts from someone parting out a set of wrecked carbs. In the worst case you'll need an entire set of new carbs to salvage what you need; not many people part them out, but it does happen. Unfortunately this is expensive
