1976 Bonneville T140V

Have a look at www.amalcarb.co.uk for new concentrics. They will probably know what you will need. The newly manufactured carbs are (allegedly) better than the originals.
As for the other bits you could try looking at the ads in Classic Bike, Classic Bike Guide or any other classic bike magazines or web sites. Google is your friend (sometimes!).

 

mikuni probably, also keihin but miks seem to be popular on older bikes from what i see elsewhere

 

They seem to be the way to go, I am no expert tho and would not pretend to be. One concern i have is that I have miks on my old Sprint and it is very thirsty, for my bike keihins are better for fuel consumption, having said that the carbs have done 45000 miles so are bound to be worn and are 20 yrs old to boot.
If you want it to look more original obviously amal are the way. I always found amal to be easy to play with but that was a few years ago