Getting beech is oddly difficult given the amount of the stuff there is around. I ended up cutting my own. That said, I have been making hand planes since the late 70s, and most of them have been made of either white oak, or maple. For the most part maple. I can think of a single one that has given me trouble. Normally using regular shop tools (mainly a bandsaw, but I didn't have one of those to start with), I set aside 45 minutes to make a functioning plane that will do good work in any format. This isn't some speed exercise of a master, it's a tiny piece of wood into which you are sawing a slot. I am not that proficient and hand mortising, though I have been at it for 35 years that I would get a mortised plane done that fast, but in a class of pretty much newbies to plane making, everyone will turn out a plane in a morning.
The Roubo era plane could probably be made pretty quickly. I never timed any of the side slot planes I made. But they are fast. I tossed off this Osage rebate to get into the dovetail plane I made the bit out of a 1/2" lathe cutter, hard to grind, but hardly ever needs sharpening. There is a maple japanese style plane, I made in the 80s under it, not a good combo, but I still use it regularly as I switched it into a thicknessing plane for 1/4" strips. I could probably make that Osage plane faster than I can unearth all the parts of a router set-up to do the same thing. If I had to choose between making a plane and installing a lockset with hand tools, I would choose the plane on speed.
So there are two approaches to all this. One is to make the plane, make the molding, and move on. The other is to have the experience of making the plane using the tools and techniques and wood of the period. Step one for the latter: build a Roubo bench... Step two is build a forge and make your own hold-downs. I've done all that stuff, but there are endless rat holes one can get caught up in if all you need are some tools.
In the alternative, maple works great Square up a block, make a few saw cuts, break out the waste with a chisel or router plane, whittle a wedge, make some shavings. For a somewhat more durable plane you can glue a wedge across the opened slot. If you do that you can reduce the thickness of the beam of the Roubo plane as the loads will be carried more efficiently.