Here are a few links of local real estate agencies that offer long-term rentals in Montenegro:
HERCEG NOVI
"Herceg Novi Rentals" - Long-term Rentals in Herceg Novi, Montenegro
TIVAT / KOTOR
"Tivat Rentals" Agencia | Long-term rentals in Tivat, Montenegro
BUDVA
"Budva Rentals" - Long term rentals in Budva, Montenegro
PODGORICA
"Podgorica Rentals" Agencia | Long-term rentals in Podgorica, Montenegro
Somewhere2rent - Long term rentals listings
Krstas Nekretnine
Podgorica Apartments rentals | Podgorica Houses rentals
PORTALS
Realitica - Long term rentals listings Realitica - Long term rentals listings
Kotor | Tivat | Herceg Novi | Budva | Podgorica
Holidayslettings.co.uk - long term lettings in Montenegro
Homeaway.com - long term lettings in Montenegro