Well, there are a couple of issues here.
Most good flat point JHP rounds are for handguns. There are no factory handguns sold in North America that are chambered for larger than 50cal, since anything larger was considered either OAW or a DD. (this is one of the reasons the Desert Eagle is only for .500" and not .510")
[Read this in a Speer reloading manual as well as from another long time shooter...either their both wrong or both right]
Anyhow, there are currently no domestically manufactured ammo for factory guns that use a handgun JHP bullet much larger than .501", that I have seen.
The 500 linebaugh is .510", but, I have only seen cast bullets for it.
There are some rifle loads that MIGHT work.
http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=741395It seams a bit shy of what you might want, since its only .510" and not .512"... I don't know and I only shoot soft lead in my BP rifles.
A paper patched .501" bullet MIGHT work...but, I would not spend alot of money on it, if I were you.
As far as smokeless, I will attest to use 9.2gr of IMR TrailBoss behind a 335-350gr .512" soft lead bullet. 950fps with winchester large rifle primers in the starline case. I have 25 of these loaded that I plan to bring to an indoor range I frequent.