UrbanMechs... rare? That ain't correct. An UM-R60L is rare, however I think they got it wrong for the UM-R60 if HBS thinks its rare. All of the major Houses have large stockpiles of them, but only assign them to militias or garrisons. The Capellans, however, do field them in front-line defensive units.
Just to check I did some random rolls from the Random Assignment Tables by creating a lance of 4 Lights (Also note that when using a RAT, and you land on specific Mechs like the Urban (depending on the Faction), you can reroll if you are assembling A or B rated units, but I am assuming here I am taking what I can get for a Second-Line Unit):
** = Second-Line Unit for Specific Factions
Salvage = Means Re-Roll on listed Factions RAT
Liao
STG-3G Stinger
STG-3G Stinger
LCT-3V Locust
UM-R60 UrbanMech**
Kurita
FS9-H Firestarter
FS9-H Firestarter
SDR-5V Spider
PNT-9R Panther
Davion
JVN-10F Javelin
STG-3G Stinger
WSP-1D Wasp
Salvage: Liao (ReRoll = LCT-1V Locust)
Marik
UM-R60 Urbanmech**
UM-R60 Urbanmech**
UM-R60 Urbanmech**
LCT-1E Locust
Steiner
LCT-1S Locust
WSP-1A Wasp
COM-2D Commando
COM-2D Commando
Mercenary
WSP-1A Wasp
STG-3G Stinger
WSP-1A Wasp
UM-R60 Urbanmech
Canopus
MON-67 Mongoose
LCT-1V Locust
WSP-1A Wasp
MON-67 Mongoose
Outworlds Alliance
WSP-1A Wasp
LCT-1V Locust
SDR-5V Spider
UM-R60 Urbanmech
Taurian Concordat
LCT-1V Locust
LCT-1V Locust
STG-3R Stinger
WSP-1A Wasp
Note: For Mercs and Minor Powers, Urbans do not get reroll opportunities, they use what they can get.