Buy rod or what ever and cut it up into smaller chucks.
I haven't priced this option, just assuming that any formed metal will be significantly more expensive than new casting material (about $15 / pound).
Since your casting anyways could you just make it, copper, lead, tin and zinc right ?
That is plan B, add lead to unknown-alloy scrap. Yes it seems the pure metals are more easily sourced (compared to specific brass alloys).
I have a collection of brass plumbing fittings I'm hoping to try casting with some day, but I have no idea what the composition is or how well they will work for that. if "Leaded red brass is typically found in plumbing applications" who knows, it might be just fine. Do you know the original use of your scrap?
Most of my original melts were old brass figurines. I doubt the alloy was intended to be machined, and is likely a bronze. Unfortunately I don't have much old brass plumbing fittings, but suspect they would be OK.
I'm not sure if your question was rhetorical?
A quick google search says leaded red brass is the most common and typically used in things such as screws , valves, fittings...
So maybe you already have a collection? I'm not sure if there is a way to test the composition of the brass, but what have you got to loose by melting it down into an ingot and seeing how well it flows...etc
No, and no collection of plumbing fittings

. There are ways to test the alloy, but not sure I am interested in going to the trouble of a "eureka" process. Frankly that is why I am looking for a source of known alloy. But ya, plan B is to tweak scrap brass/bronze (add lead) and test for machinability. I believe that most brass/bronze scrap will flow fairly well but its machinability will be a crap shoot. Certainly my first castings were tough as hell, not what I want to deal with in my various planned projects.
Just in case anyone is looking for it....I have some 2" round 360 brass and would be willing to sell some. And I probably would be willing to part with some 1" round 360 also but need to my stock. I love brass but my gosh it's terribly expensive.
Aye, that it i$. I paid a lot for the bits of bar and rod in my materials pile, not sure I want to melt them down .... yours either

but thanks for the consideration. I can buy scrap from the unwitting for under $5/pound, it's just a little more work and time and unreliable.
Dave