Grinding a tool like that is not so difficult, just sneak up on it, very little relief is required on the sides, given the shallow depth required. There is a company that sells grooving tools, I think "thinbit" is their trademark.
Kaiser Thinbit, excellent tools that I use often.
Internal, external and face grooving using modular insert holding, same tool body using different ends that fit the job at hand much like Manchester/Widia grooving tools.
Not a good tool for the faint of heart however. http://www.thinbit.com/products/grooving/index.php
I have a situation wherein I need a groove similar to what you want. It's thin, it's shallow, and it is a rare occasion when I need it. I use a cut down hacksaw blade in a small cutoff tool holder. The only stipulation here is that I do not use a hardware store blade, I use a Starrett HSS blade. There is a carbon steel blade by Starrett that I avoid like the plague. The HSS blade is shaped and sharpened just like a lathe tool, i.e. it's kept cool while it's ground.
I will concede the groove doesn't carry any load, the clip is there for a "just in case" application. But it works... ...
Its a hacksaw blade holder set at a 10:1 slope. I'll try a lennox blade first. Bill, where do you order the blade you like?
That looks almost as good as what I do. The only debate is that you must remember the "set" of the teeth. It will make the cut a little wider than the blade thickness. I break the blade off, it's from a used blade. (Nothing gets thrown away in my shop) Then treat the blade as a very thin cut off tool. Model builders,, huh!
As to aqusition, I stole (literally) them from the maintenance shops at a steel mill I used to work at. I have no idea where they originated. Sorry I can't help more there. Looking to commercial supply houses is the best I can do. The Lennox would be a likely candidate, they make pretty good tools.
I have a hacksaw blade holder, but I grind the end of the hacksaw blade into a parting tool like end. No teeth I remove them from the
end I'm going to cut with. So it just cuts from the top edge same as parting blade.
My blade is straight in the tool holder. No angle up or down.
Gonna have to check out those hss blades as I've just used the cheap blades and just on aluminum. brass etc . Not steel.
I will heat the end and quench it if it won't hold an edge, then it usually will cut better.
I also have parting blades ground thinner. Latest one was for a 3d printer extruder body. I ground a hss blade to .055 to machine the fins.
Those blade holders are made from a chevy crankshaft, the one for the hacksaw blade has a cold rolled steel piece bolted on that has the slitting saw cut to hold the blade. The notch in the upper right of it in the first picture is an oil passage from it's days as a crankshaft.
The china blade is in dovetail grooves and has brass inserts that the bolts push on to hold the blade.
I have ground a piece of hss for this but when I first started I just plunged in with a thread cutting tool to depth and then used a hacksaw to clean it up. Doesnt take long when its precut because the hacksaw blade self aligns.