you should be able to find display cases for various things online but this is kinda specific and you probably wont find a specific wedding cake knife case.. call local trophy and award shops they will have an idea what to use and may be able to put it together for you..

Hi - have a look at some of these box frames :)

https://www.google.co.uk/search?q=shadow...

And... here is where you can purchase them from :)

http://www.alibaba.com/product-detail/Sh...

http://www.amazon.com/b?node=3019281

http://www.lulusoso.com/products/Shadow-...

http://www.ikea.com/gb/en/catalog/catego...

http://www.innovateframe.com/pages/Shado...

Hopefully you will find one that you like :)

You could perhaps search for a shadow box.