Yeah, that delay is the worst. What saved me last time was calling a few local machine shops with the CAD file. A couple of them had round stock on hand and could turn a simple flange around in like two days. It helps if your design can use a standard bar size for the main bore.
Yeah, sticking to common materials like aluminum or 1018 steel makes a huge difference. My go-to shop keeps a ton of 2-inch round stock on hand, so anything designed for that diameter gets done super fast. I always tweak my designs to match what they've got sitting on the shelf ready to go.