First off - welcome to the forum. I see you've been here a while; good to see your first post.
You know, since the frame is pretty much the same, but the radiator shrouds are different(ish), I can't help but wonder if the simple radiator guard wouldn't work. HT has this one.
Were you thinking along these lines, or looking more for the nerf bar product? Even those might work, unless you have experience that says otherwise, though how closely they would conform to the 600 shrouds may be an issue.
Have you got any photos that we can see, particularly frontal and frontal 3/4 views? Might hell judge what will and won't fit.
Dual Star also makes a simple radiator guard, but I have no idea what their current status is WRT inventories and phone answering.
I'm still not clear on what type of protection you would like to go with. The "frame" type protectors that Tom indicated, which would offer some protection in a situation where the bike bites the ground, or a screen / mesh type protector to protect again rocks and road debris.
Here's some food for thought. Below is a photo of a KLR 250:
Here is a set of mesh type radiator protectors for the KLR 250:
Here is an image of a KLR 600:
Compared to a Gen I KLR 650:
With only images for a comparison, I'm thinking you might have more chances of success looking to the KLR 250 for adaptable components.
Something to consider maybe. If actual framed protectors like those offered by Happy Trails are more in line with what you are looking for, you might consider these:
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