Stencollector here on Milsurps and located in Manitoba, Canada, has original Canadian transit chests for sale here in (2015) which were made for the C No 7 Lee-Enfield rifle circa 1944-1950. They are similar to the No. 15 "Sniper" chest except:
1. They are not as tall thus there is room for neither the scope case No. 8 Mk. I (steel) nor No. 8 Mk. 2 (canvas), nor the Scout Regt. Telescope.
2. They have wooden horseshoe shaped protectors around each of the two latches.
3. The carrying handles are made of web rifle slings rather than the leather used on Britishand Canadian No. 15 chests.
4. Inside there is a block fitted to the side with vertical holes for cleaning brush etc.
5. The top of each of the two tethered blocks that drop in to hold the rifle have a slot in their top for the cleaning rod
6. There is no pivoting block or fixed blocks to hold the No. 8 scope case in place (which would not fit anyways)
Although not exactly the same as the sniper No. 15 chest, they are the economy version (about $100-125 each vs. $500-1,000 each) for reenactor and can safely transport a No. 4 Lee-Enfield. Remember that a sniper would not usually lug around a transit chest. Note that the No. 15 chests were designed for "N" Normal length butt. If your rifle is fitted with an "L" Long butt, it might or might not fit.
If you want to make a replica transit Chest No. 15 of your own, Stencollector also has original WWII hardware (hinges and hasps) salvaged from WWII transit chests from a surplus dealer whom Stencollector and I knew. The surplus dealer left a huge stack if these chests outside for many years and some rotted. As I recall these were BREN transit chests but the hardware is the same as used in the No. 15 Teansit Chests. The British Army (and Commonwealth nations) used both British made (3 screw holes on each hinge arm) and Canadian made (4 screw holes) transit Chests No. 15.
Moore Leather in Scotland makes excellent reproduction leather goods for the sniper rifles including the handles for the No. 15 chest. I bought one pair of handles. You can easily tell it is a repro, but it is serviceable!
By the way, a museum tip - Don't lift your original No. 15 Chest by its original leather handles - especially if it has rifle, scope, Case No 8 with scope and Scout Regiment Telescope! The leather is now close to 3/4 of a century old and is usually dry and partly torn or frayed. Even if it looks mint, it is not. If it breaks, you cannot repair it must either leave it broken or replace it and the value of the chest drops considerably either way. If the original leather carrying handles break, you will likely learn some new swear words.