Here 's a link to a site with orifices. I can tell you though that from my experience going through 5 different sizes and PLENTY of gas volume. I get about 3.5 inch solid blue flame but still take 45 minutes for a boil and it want be a rolling boiling if the lid isn't on. I called any talked to the guy that runs and makes alot of the things you see on this site and has been in propane for awhile. Its pretty clear that these burners at low pressure will not cut it. He's rating on these burners in 25,000 btu's at low pressure. I have decided to put my boil burner on high pressure which I know works well and keep my HLT and MLT on low. I had already made my stand for these burners and really not feel like changing it at this time. I have some picks up you can check out. Below is how I made orifices if you interested. I never bought any I was going to from this guy but didn't after talking with him.
So I just made my own orifices which is actually pretty easy. Acehardware has everything you need. You will need to buy a wire bit to size to like #55 is the one that I found to be the best. You buy a 1/8 brass pipe fitting and tap out the inside of it. You then buy a brass screw to fit your tap size. Drill a hole in the brass screw VERY carefully with your wire bit. Cut the head off the screw and put some gas tap on it. thread it in and you have an orifice.