At the risk of answering for Andy -- I have made lugs like this and I assume his process is much the same as mine.
Hole saws are definitely available. if the lug socket is for a 1" tube, you use a 1" holesaw. 1-1/4" tube, 1-1/4" holesaw. Got it?

The holesaw isn't sized to a tube ID, it's the tube OD. Or strictly speaking it's the lug ID, which is based on the tube OD plus a few thousandths for brazing filler clearance.

I once made a set of lugs with BB shell that were sent to Japan to be masters for a new line of investment-cast lugs. Took me a week of long days, could have build a few entire frames in that time. Then they lost the BB shell, asked me to make another! My boss said no, just let them make the BB shell however they think best. They make plenty of BB shells, right? The resulting cast lugs were great, but the BB shell they made was horrible, with several small screwups and one huge one -- we had to grind out the chainstay sockets with a hand-held die grinder on each one. Oval stays, so you can't do it with a reamer or other simple round tool. Nasty job, sending up showers of micro-fine super sharp needles of steel, that get in everywhere... It took skill to do it accurately so we couldn't just hire disadvantaged youths to do it. After doing a couple hundred shells that way, we were definitely wishing we'd made another master model BB shell when they asked. (This was the '80s, so if CNC was an option, we didn't know about it. Prolly too expensive and/or large minimums.)

That's when we figured out that the IC casting staff at this Japanese maker of bike lugs weren't really bike people, they were manufacturing people. They could make whatever you want, but don't ask them to design it!

Mark B