Kawasaki calls it a "DIAPHRAGM,VALVE"
The Kawasaki Part Number is: 43028-1062
It's the same on all KLR 650's from 1984 through at least 2015
Partzilla wants $123.11, the best price on eBay that I could find for this Part Number is: $169.72. Many other sources fall in between these two if I search with Google.
I'm pretty sure that the same part for a carbureted 2003 Harley-Davidson Low Rider would work. But I don't have the Harley Part Number for that. I'd guess someone else may be able to help out with this, or maybe some other application that uses/used this carburetor.
Also, you can find complete carburetors for a KLR650 on eBay for right around $100 if you have a bit of patience.