Getting ready to have a custom exhaust system built from the cross-over back. I couldn't find anyone that sells a Toyota O2 sensor bung to weld into the new exhaust piping. After talking to a friend that works at the local Toyota dealer about where to get one, he says why don't you just make one? I hadn't thought of that Jason, thanks for the idea. So here's how to make your own O2 sensor bung.
I started with a piece of 3/8 steel and marked the outline with a gasket and drilled and tapped some holes (8mm x 1.25):


I used some exhaust studs from the dealer that were left over when I was putting on the ORS cross-over.


Then I started cutting it out with a cutoff wheel on an angle grinder:

After using a grinder and beltsander to smooth it out:


Now that was one bung, but I need two for the 5VZ right. The first one took me about 2-3 hours to make so I decided to try cutting an old one out of my old 3.0 exhaust pipe and using it. That took about 2-3 hours too, counting replacing the old studs and smoothing it out with a grinder and beltsander too.

Here's the two side by side, the one I made from scratch will have to be welded in parallel to the pipe since it's not curved to the shape of the pipe: