Examples of the Midget Submarines and Submersible Craft are held within the collections of several museums around the world.  

An excellent model  exists of the Welfreighter created for  Shelvoke and Drewry Ltd and presented by them to the National Maritime Museum in Greenwich. This is the only surviving representation of the craft ( none of the real Welfreighters are known to have survived.)

X24 - the X craft that was involved  in two operations to attack the floating dock in Bergen harbour  in 1944 is preserved at the R.N submarine Museum at Gosport.

XE 8 ( Expunger) - was raised from the seabed off Portland in 1976 and  it is thought still awaits restoration at Chatham Historic Dockyard in Kent.

X51 ( Stickleback)  - Built in 1954 and  subsequently sold to the Swedish navy is now within the Imperial War Museum collection at Duxford.

Three Welman submarines are known to exist. Two of these are craft recovered from the operation "Barbara" to attack  Bergen  harbour in November 1943. One, salvaged in the 1970's,  is on display at the Marine Musem in Horten,  Norway. The other  is the Welman 46 used by  2nd. Lt. B. Pedersen  who was captured during  the operation.  The craft was recovered by the Germans, and was transported back to Germany, for evaluation. It is still on display in Germany.. A third Craft,  Welman 10,  was salvaged from the waters off  Rothesay in the Clyde and can be seen at the Royal Navy Submarine Museum in Gosport.

A Welman was sent to the USA in 1943 for evaluation. I understand it is  still preserved in a Naval  Museum Collection there.

A Mk I chariot is said to be on display, still, at Kylesku in Sutherland, overlooking Loch Cairnbawn - Port XXZ - the training base for all Midget sub operations in WW 2.

In Sydney,  Australia, several WW2  vessels are  under preservation. HMAS Krait the  most famous of the Services Reconnaissance Department's  "covert " fleet is  one of these..  Also preserved are examples of the Japanese midget submarines which attacked the harbour in 1942.

There is an example of the German "Biber" on display  next to the  RN submarine collections at the RN Submarine Museum in Gosport.
Photo courtesy S&D archive. Copyright reserved
Stanley Quin M.D. of Shelvoke and Drewry shakes hand  of The director of the National Maritime Museum Basil Greenhill at the presentation of the model to the Museum in 1977. The Curator of Ships Models Capt. Neville Upham looks on.