I had to replace the vertical oscillator blocking transformer in my DuMont RA-102, and the folks here supplied the right cross-reference to order one from Play Things of Past. This thread has more details:
http://www.videokarma.org/showthread.php?t=268125
The RA-103 part may be a little different, but these transformers are out there, if you need one.
Regards,
Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html