I have just got into this, and today have a working system up and running using the brand manufacturer in etsy mentioned above.
However as a beginner maybe I didn't do enough research first, and should have focused more on the ancillaries rather than having the brand made up. I suspect others may have done the same.....
I approached this from the wrong end, I got excited and had the brand made first (very good, works fine on leather and wood, no probs there), Then made up a handle and rod to hold it, then decided for more repeatable temperature control I would prefer electric... wasted a bit of time and effort along the way.
After making a fine wood handle and played with gas heating, I bought a heavy duty 300w soldering iron, and made up a controller using a spare room light dimmer that I had kicking around. I noticed that on sites related to wood branding these were commonly mentioned. This rig works fine, I am a) always near power in the workshop, and b) not doing a mass production run, and c) only using a smallish brand on the bases of items.
The Iron I bought came with a large bent chisel type tip, the diameter of the tip where it goes into the iron is 14mm. A chunky piece of copper! I already had the brand, and had, without much thought, specified the thread in the back of the brand, as at that time I was only thinking of making a home made handle and the actual thread wasn't really critical.
Now I had the iron. I had to modify the bit and drill/tap a thread in it to take a stub thread to attach the brand. Took a while.
I then noticed you could buy a similar looking iron, similar power, (E*ay) with a load of screw in pyrography bits for the similar price as the Iron I was modifying. I should have bought one of those, measured the thread on the brands in the kit, and then specified the thread to the chap making my Brand. Curses!
So that is my learning :
I would go electric, with a high power iron and then use a controller especially if you have the spare components to make one cheap.
I would look at the pyrograpy kits which is essentially a big soldering iron with screw in brands with it.
Then I would order up the brand itself with a matching thread to the pyrography iron.
Have some scrap wood ready to practice on before doing the deed on a valuable piece. I have plenty of scrap bits of wood, seems to be my largest product actually.
This is probably all crashingly obvious to more experienced folk, but I just liked the idea of the brand and gave it a quick try without much reseach, perhaps this post will help others just giving it a go like me.
Good Luck,