A simple way to find one is to check the Digi-key or Mouser online catalogs.
I entered "transistor PNP TO-3" into the Digi-Key (
www.digikey.com) search and
it gives a few options, depending whether you need 250V / 17A or 100V / 25A.
The 2SA1962 / 2SA1943 / 2SA2510 would be likely candidates. They are
all in plastic packages that are designed to be compatible with the TO-3
mounting holes.
The same search on
www.mouser.com gives a different list - it doesn't allow
as much refinement. But they carry the ON Semi parts such as the
MJ4502 (100V / 30A), MJ2955 (the 2N2955 is the PNP equivalent of the
standard 2N3055). The 2N5684 is rated 80V / 50A / 300W in a metal TO-3 case.
Meanwhile, here is a handy page of transistor ratings and NPN / PNP equivalents
from Central Semiconductor:
http://www.centralsemi.com/PDFs/products/LSSGP082.PDFIt doesn't show a PNP equivalent for the 2N3771 (50V / 30A) but the
2N4399 (60V / 30A) would probably work.
