The industry has come a ways since the only replacement hoods for vintage non-aero brake levers that you could find were "merde plastique" from Euro-Aisian Imports (EAI) or Cane Creek.
Here is what I have found:
Dia Compe- it looks like Dia Compe now offers their brake lever hoods in color "Amber" ...looks like translucent gum to me. Both Dia Compe lever styles. I have an inquiry to one of their stocklists to see if I can purchase a couple of pair.
DC204QC COVER Amber | DIA-COMPE
Soma Fabrications- translucent gum and black hoods for vintage Campagnolo with Soma logo. Quality looks good, but I have not seen them in person.
Brake Lever Hoods for Vintage Campy | SOMA Fabrications
Rustines- translucent gum, black, and white hoods to fit Campagnolo NR/SR, Mafac (2 styles), Weinmann/Dia Compe, and Universal. Some styles are available from Velo Orange, and Rustines is easy and pleasant to deal with directly. All styles not always shown on their website, but an inquiry will get you
a quick reply as what is available and when. Rustines logo and very nice quality.
http://www.rustines.fr
https://velo-orange.com/collections/brake-parts
"NOS" Campagnolo NR/SR brake hoods- These are found easily on eBay though everyone should understand that most are not genuine new-old-stock. Both the older globe logo, and the newer shield logo styles on offer. Quality and price vary...
Legend has it that someone in Italy acquired the original molds from Campagnolo and is/was manufacturing reproductions from these original molds. This may be an urban legend- maybe someone here knows more about this story.
By all accounts, the reproduction NR/SR hoods from Hilary Stone are the nicest. I purchased 2 pair from him and the quality is excellent. Hilary sells reproduction Universal hoods and the little adjuster nipples that go with them as well, but they don't look like translucent gum to me.
At some point, I'll buy a pair and post a picture of them alongside a NOS set.
Hilary Stone Spare Parts Brakes
Seller doniselliciclimartin on Italian eBay sells reproduction Universal brake hood levers and adjuster nipples...perhaps the same item that Hilary Stone is selling. Not yet seen in person by me...
https://www.ebay.it/usr/doniselliciclimartin
For very early brake levers, David Beck- a regular poster here as "iab" makes a reproduction Vittoria brake lever hood. I'll let him explain the historical background of these- I'd probably get it only half right.
https://www.flickr.com/photos/681231...in/dateposted/
Then of course, there is always the genuine article. If you have the patience and the money a new-old-stock pair or a well preserved set will eventually turn up that matches or fits your brake levers. I've purchased NOS brake lever sets just for the fresh hoods. If your levers are very vintage, or not common,
be prepared with your credit card and strike fast...
There are probably others- please post other sources if you know of any...