Here is an idea for you.
If you happen to be ordering something from KEH.com then you might want to consider adding this miscelaneous brand "A" 2X teleconverter for Condition EX $3.99 or Condition BGN for $1.79.
...then either remove or break out the glass elements. Then you will have a 25mm extension tube that has all of the contacts.
Note 1: It most likely would not be a good idea to order one of these by themselves because the shipping charges would be excessive for such a buy. Instead add it to the cart if you are already making another purchase.
Note 2: If you go to the link above then click on the image to see that it is indeed an "A" type teleconverter.
Note 3: Although the link below does not state that it is an "A" type teleconverter the image shows that it is. The prices are the same as those via the link above.
Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'
'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx