I am trying to identify the red color output transistor on my Zenith
model sy2551s.

Sams' Photofact lists it as:
Item # Q5103
Mfr. # 121-1291-01
NTE Part # NTE157

The stamp on the body of the transistor consists of three rows of id as
follows:
The top row is a logo that looks like an R
The second row reads: C5147
The bottom row reads: D 650

R
C5147
D 650

The bottom row of the green and blue transistors say D 651 instead,
but I don't know if that's important.

Finally, where can I find a replacement? Do they have these at radio
shack, or another walk-in electronics place? I don't know if i can
order 1-2 transistors online (shipping may cost alot too).

Thanks for any help.