My reserve is front mounted on my Parajet, http://shop.flybubble.co.uk/gin-gliders-reserve-outer-container should get the mayday in it but might be a squeeze.. if you wanted it in a new container then maybe buy one from the loft and they may pack it for you too?
Front mounted is by far the best place in my opinion as you can see it at all times and can throw with both hands if needed.. but obviously better throwing to the side the bridle goes if possible!
Like this..