Paul Manganaro points out that the Monarch roll frame includes one
compound gear with a bevel gear on one side and a spur gear on the
other.  The stock gear suppliers such as Martin and Boston Gear won't
sell the compound gear as one unit.  Nevertheless, it appears that one
could purchase the bevel gear and the spur gear separately, then modify
them a bit to enable fastening them together.

Bevel gears are not interchangeable; they must be purchased in matched
pairs.  They will probably use a pressure angle of 20 degrees.  (As
long as you are replacing both gears in a pair, it is not critical
to match the original pressure angle.)

A different procedure is needed to determine the pitch diameter of a
bevel gear.  I would suggest looking directly at the back of the gear.
While it's difficult to tell the pitch diameter exactly, you can make a
good estimate by measuring the diameter a point roughly halfway between
the roots and the tips of the teeth (as you look straight at the gear
from the back).  You'll probably get a better estimate by using the
larger gear.  The pitch diameter will likely be some "clean" number
such as 0.750 inch or 2.500 inches, so round off your best estimate.

As with the spur gears, the diametral pitch, P, is determined by
dividing the number of teeth, N, by the pitch diameter, d.  Gears are
usually organized in catalogs according to diametral pitch.  I hope
this helps.

Best Regards,
Tom Chase
Minneapolis, Minnesota