I saw some nice simple one in Woodies at the weekend. Also I saw some nice fireside accessories in our local old fasioned hardware store.
For fire guards, go for the finemesh if you are buring smokeless coal or timeber blocks which are inclined to spark. Also make sure that as much of the open fireplace is covered as possible.
If you have small children you may need a second coarse mesh guard which can be anchored to the wall.
aj