They definately exist - i've got an MFi head on my orion, and it runs an EFi inlet. Theres an 8mm thick aluminium sandwich plate that sits between the head and the inlet.

If you cant find none on ebay, theres a company called 'ferriday engineering' who sell them. Along with a variety of other conversion plates/decompression plates etc...

Think you're talking about £100 for a new adapter plate from them, though....