If you can get to the SSA championships 1-3 Aug at Addington Manor you will be able to pick up a habit there. There are usually quite a few trade stands selling side saddles, habits, hats, canes, etc.
It's also a great chance to watch over 60 classes ALL ridden side saddle
Great day out in a beautiful setting, the side saddle lot are very friendly too and don't mind if you ask them questions!
If your friend is a member of the SSA they usually include a for sale/wanted section in their newsletters.
Remeber though anything to do with side saddle is expensive!!!
Tell your friend to look for a nice second hand habit rather than a new one which can cost around £550!!!
The old ones are better quality and because they were originaly tailor made to fit, the cut of the cloth is far superior, look out for the classic names, Roberts and Carroll, Busvine, Bernard Weatherall, they are the best