Training other roles is useful if you have say a 5* nordgen, because you don't want him to hit that 6* training slow down. Also I have players who get good ratings in 2 different roles, you just have to build up their stats the right way. As to your original post, I would say just keep checking, especially at times you normally don't. They are difficult to find but getting close to the end of the season people will be offloading some players you can get for very few tokens