I don't have anywhere locally for firebricks either. I ended up ordering 3 from High Temperature tools. With the flat rate shipping it was about the best price I could find delivered.
http://www.hightemptools.com/firebricks.html
Just my two cents, i'm been using a two brick forge for a couple months, so I'm no expert, but I've had pretty good luck. The hole on my 2-brick is about a 1/4 of the way back from the front and on the bottom of the chamber so it swirls under the blade and then up around the cavity. If I'm treating a short enough blade I usually have another fire brick covering the opening on the back of the forge to hold more heat in.
No matter what you do the hottest place in forge is going to be where the flame enters the cavity. With that in mind I move my blades around a lot during heat treat to get it even across the full blade. By having the inlet hole closer to the front of the forge you can pass the whole blade past it consistently. If it was in the back I wonder if you would have issues with the tip getting to temperature before the rest of the blade comes to temp. Just my thoughts.
-Aaron
Aaron,
Generally the tip is the thinnest part of the blade so it is usually the 1st
to come up to temp. That is provided the entire chamber is at temp., I would
ONLY use this method with the simplest HC steels in the 10XX SERIES,like
1084, and those below it, 1080, 1075, 1070, etc.
Do keep in mind, that when you HT this way, that you MUST GET THE ENTIRE
BLADE TO THE DESIRED TEMP!
2.) The motion you use when quenching is vital, you want to put the entire blade in the
fast quench oil as quickly (and safely) as possible, then aggitate. This is the most critical
part of the quench, as you ONLY want to move the blade in a back and forth motion.
NEVER SIDE TO SIDE! The wayI do it, I emmerse the entire blade once I pull it out
of the kiln, I go straight to the oil, if yoh don't put the knife all the way in the oil,
YOU WILL HAVE A FLAME UP, now this isn't a major deal, unless you do it all
the time, your oil will not last very long,now once in the oil, I pay close attention to
how the boade is in the oil and how I agitate the blade back and forth, while I am counting
(usually) OUT LOUD! That way no one will try to talk to me, and I count just like this,
1, and 2, and 3, and... all the way to 30, even a bigger blade should be cool enough to touch
but DONT UNTIL YOU ARE SURE ITS COOL ENOUGH!
HOPE THIS HELPS,
Rex