Lectron currently sells a carb kit for the XR650L (should also fit XR600R with a little work), and XR650R.
https://www.lectronfuelsystems.com/xr-650-kit.html
I'm currently running an Edelbrock Quicksilver on my XR650L and it's a similar jetless design, except it has an accelerator pump and external, no-tool needle adjustment. Idles and runs better than the XR600R and stock XR650L carb I've used, and it's not just because of the accelerator pump (but that does make cold starts much quicker).
If/when my Edelbrock wears out or something breaks (no new parts available), I'll be going with the Lectron.
The story of three wheels and a man...