There is an excellent web site where modifications are available, among them the type of roster files that you are looking for. This web site is:
http://web.mac.com/sixwilsons/iWeb/OOTPMods/Main.html. Click Templates and Rosters. Also, to read how to install these modifications, click Mod Installation Help.
There is another resource that I can recommend for historical play. This is the Lahman Database (it's free, but throw the guy a few bucks if you are feeling charitable). This web site is:
http://www.baseball1.com/. The manual contains some general instructions on loading historical databases, but one of our members wrote a terrific "how-to" on loading the Lahman Database; it can be found here:
Getting ready to make history.
Finally, you will want to look through the sub-forum called Rosters, Photos, and Quick-Starts, part of the Mods forum. Pay particular attention to the sticky threads at the top of that board.