Not much of a guide for this, it's all about persevering when playing the The Casino.
You get to The Casino just through natural game progression. When in, there are a number of slot machines, all the same. Just keep pressing square to spin the reels. It will cost you $10 a time but I found I'd always win before running out of money, starting with a balance of about $2000. Not sure if it's set to do that or not so don't blame me if you go broke!
There are further opportunities to get this trophy in the game but I believe The Casino is the first.