Is that your measurement presumably taken with a digital caliper? I've found a black spokes that's 2.2mm x 0.9mm that's a J bend. Would that do?
Edit: Are you absolutely sure it's 3mm wide? That's larger than the spoke hole in most hubs so how does that get through? I think that's why you tend to find bladed spokes are straight pull.
If you're 100% sure of those measurements I can't find anything on the websites I use for looking for spokes. I've not found any that are wider than 2.2mm or thicker than 0.9mm. As for the spoke hole in the hub i don't profess to know every hub on the market but the collection i have in my shed don't go any larger than 2.6mm so your spoke wouldn't fit any of them. What hub have you got?
It looked promising, but the site doesn't specify dimensions (only length), not width or thickness.
Couldn't go wrong with these could you? (?)
https://www.ebay.co.uk/itm/305472132166?
"Please allow slight manual measurement deviation for the data."
Just replace with a decent DT Swiss Aerolite
Does it matter if 2.3mm as opposed to 2.9mm? Will the wheel become unbalanced? Will you leak watts?