I specialize in helping people buy and sell houses in Scarborough, but here are a couple of companies that specialize in rentals you can check out:
Drinan Properties (South Portland) 207.799.0829 / http://www.drinanproperties.com/houses/housesscarborough.html
Maine Properties Inc. (Scarborough) 207.883.3753 / http://ahn03.com/maine/outside_home.asp
Seashore property management (OOB) 207.934.3400 does a lot of seasonal rentals, and I have copied the link to the one year round home the have for rent: http://www.seashorepropertymanagement.com/vacation-rentals-homes.asp?cat=3693
The Curry Agency (Scarborough) 207.883.6444. Here is the link to their winter rental page that you might be able to negotiate for longer term - quite a few to choose from! http://curryagency.com/rentals/winter-rentals
Best of Luck!