Perhaps you might tell us a little bit about what the transistor is doing,
why it needs to be replaced, what kind of circuit it's in? It matters, you
know. In some circuits, you can't even replace a transistor with another
one of the same model number, without testing and selecting it for
particular values. In other circuits, it barely matters what transistor you
use as long as it's the right polarity.
The TIP120 shows as still being in active production at On Semi (who took
over Motorola's line of discrete semis). So, barring the selection issue I
just mentioned, one thing you might replace a TIP120 with would be another
TIP120. Is there some reason that alternative is out of the running?
As long as you're at it, how about telling us a little bit about yourself?
Say, a first name? Makes it easier to be friendly.