Graf and Sons , Brownells has them many places you could even try Ebay , not sure what you willing to spend but I bought a set of Redding from Brownells for around 80 shipped .
If its SAAMI spec you can get them anywhere that sells Redding dies...and I think Hornady makes them too...I got mine from MidwayUSA...everything Midway has for 280 AI is for the SAAMI spec version, despite the name confusion....I compared part numbers (Redding part numbers)
If its original spec you're after....you'll have to either buy used or have them custom made, Redding does this too.
I have a few sets of original bought from brownels and rcbs no wIt no customizing, and your right Hornady does make SAMMI dies for like 50 bucks avalible most places
I'm in the process of moving this very week, but I believe I have a duplicate set of 280AI RCBS dies, and one is unused. If you're interested, when I unpack in Maine, I'll sell very reasonably. I sure didn't intend on owning TWO!!