Bending thin wall tubing to a tight radius require special tools that
support the tubing while it is bending.  The tighter the radius, the
more support needed.  You can get moderate bends with a close fitting
tubing bending spring.  To get the really tight bends typical of player
elbows requires a dedicated die set.

It is really quite easy to make them by soldering two mitered pieces
together.  You can get a miniature miter box made by X-Acto from a
hobby shop.  They also make a fine-tooth saw that fits the box which
works well for thin wall tubing.

You can cut off the pieces completely or cut a 90 degree notch almost
all the way through, leaving just a bit of brass remaining to hold the
piece together when you solder.  The cheapie little miter boxes are not
especially good at making the precise cuts needed to do it this way,
so you may need a better miter box if you need to make a lot of elbows.

You can make tees by cutting or grinding the end of a tube to the
outside radius of the tube to which it needs to be attached.  Then
solder it to the other tube and drill through after soldering.  You can
make asymmetrical tees this way, too.

Best regards,
Spencer Chase
Garberville, Calif.