You can replace main qa-styles.css with your rtl stylesheet. Just name it qa-styles.css and it should work.
I have one RTL stylesheet designed for my client. However it hasn't been designed for Snow theme and needs to modify in most case. If you want I can provide you may be it could save some of your work. But I prefer to start with original Snow theme stylesheet and just update only RTL related classes which is more easier than modifying other one.