I believe that washer would be made of felt, not sure that it's easy to come by.Those carb rebuild kits you've got usually aren't made to the exact specs of the original brass hardware, and can often lead to tuning issues down the track. If you still have the original brass hardware from the carbs, and it is in usable condition, you would likely be better off cleaning it up & reusing it.The link below has some handy info that should be relevant to 087A, 022A & 627B carbs.http://blacksquaremotorcycle.com/wp-content/uploads/2015/02/HOW-TO-REBUILD-KEIHIN-CARBURETORS.pdf
Those felt washers are not a part you easily find. Fortunately someone has remade them and you can get them here... http://www.motorcycleproject.com/
I still have the old one's but some of them are pretty bad. For the most part the old main jet is fine but the idle jet and slow jet seem to be in the worst shape. Would you recommend mixing and matching, going with the old one's or stay with the new one's? Also, I want to run pods so will be rejetting later down the line. And I do have that link and have been using it! I also have the shop manual which was helpful when disassembling.
What do you mean by pretty bad? As long as they aren't visibly damaged or corroded they're likely ok, even if a bit tarnished. A soak in some carb cleaner or acetone, followed up by running something like a 0.010 guitar string through all passages, followed by a blast to compressed air to ensure everything is clear & you should be set.
Ok, I have pipe cleaners that I will use and re use the one's I have. The slow yet looks bad since it has that green layer around it. I have a round of tests coming up but I'll try and post pictures of how they look before/after