We bought them frozen from The Fresh Fish Place in Port Lincoln.
I Googled to find a few recipes ...
http://www.aww.com.au/food/recipes/2008/2/tempura-soft-shell-crabs-with-aioli/
http://www.sbs.com.au/food/recipes/tempura-soft-shell-crab-fried-chillies
to get some ideas.
If you need to clean the crabs here was a short You Tube clip ... I discovered that we needed to clean ours :-)
https://www.youtube.com/watch?v=Ytfb5yal5pM
We ended up coating our whole soft shell crab with a product sold through The Fresh Fish Place in Port Lincoln, by a company called Squid Inc ... lemon and pepper seasoning.
John shallow fried the whole soft shell crabs for a few minutes. I stir fried some capsicum, spring onions and brocollini with garlic, ginger, chilli and added a little bit of coconut milk at the end.
The photo doesn't look great but it tasted really good :-)