357 max cases are available, but some times they are not. they are usually have a large run and they wait until the sully dries up and then make another large run. So they are not available all the time, but enough to get a large supply to last a while. I bought 600 cases in the last run, then it dried up and now they are back again, but I do not need any. While loaded 357 Max ammo is not widely available, it is available through the internet.
I have cut a chamber and the quality is fine. I really did not legthen the throat, only cut the chamber a little longer. I did it myself, by renting a reamer. It shoots 38 Specials, 357 mags and 357 Max ammo with more than execptable accuracy. Most folks that have done this have found this to be true.
The 357 B & D is a 44 Mag case necked down to 357, so it is the same length as a regular 44 Mag and shorter than a 357 Max. You can cut the 357 max chamber yourself, but I would hire the 44 B&D done.
I think the performance is about the same, but I prefer the 357 Max, because I can still shoot 38 Specials, 357 mags and 357 max in the same gun + I do not have to form cases.
Good Luck and Good Shooting
BTW I love my 357 Max and I think of you do a little research on it here, you will find many others feel the same way.