>If not, does anyone know where to go to find a really good howto on making them yourself?
I run them through a table saw (with or without a groove) before I assemble them. The top bar run through at 45 degrees on each side works well.
But I think the wedge broken out and glued and nailed back in is the simplest.
>By a centre support do you mean a rod or even wood wedge?
> Is the idea that without something like that on a deep frame the brood comb could sag or disfigure in the warmth of the hive?
Yes and when it's new and not attached to the sides yet it can get quite heavy while the wax is quite soft.