I had the same problems finding anything that starts with "b" in the US of A so much so that I had to have my brother buy me the stuff I needed in europe. The 2N and MJ or MP are the types commonly found here in the US. The bc559 is just a vile to-92 and the only thing it has going for is an hfe of 400. The bd139, which I hate, is your standard semiconductor used for driver stage. I found much higher quality devices in the japanese models from Toshiba and others. So, if you are building from scratch there are several alternatives to those transistors. If you need replacement parts is a different story. I don't want to push anything BUT I have a few bd139 and some bc560 which would be just fine, and better, as a substitute for the bc559. If you let me know what are you trying to do I can be more helpful.
Except if you need heatsinking the BD139, there shouldn't be any problem in using other transistors like the 2SC3298. It would only be a question of reversing the pins insertion, leaving the metal tab towards the other side.
To check on the pins you can use a DVM, though it's troublesome. Those having hfE meters would simplify the job.
I couldn't check on the MJE340 pins though.
The TIP types might be noisy on some positions.
On the low current types, usually having the base pin in the middle, it would only be a question of reversing the body.
Going for larger bandwidth types maybe a good thing.
In any case, Mouser does stock some European types, like the BC559 and BC550. The BD139 is not listed, but the 2SC3298 and MJE340 are.
At least this shouldn't stop you from going on with your project. What project is that?
2n3904 is an npn transistor is it not? I do have some 2n3906 in my junk box maybe I will try those in place of the bc559.
The project is DOZ ya I know its not an up to date design. I plan to build an Aleph 5 later when I can afford it. I still haven't finished my A40 but I have almost all the parts for DOZ in my junk box. So it will cost very little for me to attempt. For those interested this is where I found the PC board layout etc http://www.diyaudio.8m.com/Bebet/bebet_sch.html
I'm not a fan of DOZ but like I say I build it cheap after all how do I really know unless I try!
My bad 2n3906 is what I meant!
In my opinion, if you have to put up with 80w dissipation and decoupling caps and etching boards and hard to find semis you may as well go for a better design.
Anyways, good luck to you.