The faintest galaxies in Messier's catalogue are magnitude 10.1.
The attached list is from the SAC ver 8 database and contains 135 galaxies brighter than magnitude 10.2. Dwarf galaxies are not included.
If Messier and Mechain had searched both the northern and southern sky "properly" they would have seen most of these galaxies.
The columns in the list are:
OBJECT Name, NGC or IC number
OTHER Messier number (there are 40 Messier galaxies)
TYPE galaxies
CON Constellation
MAG Magnitude (faintest are mag 10.1)
SUBR Surface brightness (mag 15 is difficult)
SIZE_MAX in arc mins
SIZE_MIN in arc mins
PA Position angle
CLASS elliptical, spiral, irregular etc
RA Right Ascension
DEC Declination
N-S 20 galaxies are north of dec +45, 13 are south of dec -45
TI Tirion star atlas map (there are 26 maps)
Refr: http://www.saguaroastro.org/content/downloads.htm