You DO NOT have to buy the 99 match player contract from the catalogue.
It can be bought from the transfer market and you still get the achievement.
Just search for a Gold contract, minimum price 1000 and you should find loads of 99 match contracts. Then just apply it to one of your players and you should get the achievement.
This helps people who have already got the achievement on the 360 version of the game and do not want to spend months leveling up so they can buy another one from the catalogue.