Update 1: Introducing the Video Coding Engine (VCE) article has a table "detailed description of the AMD products and the VCE version they are powered with" listing specific products. Would it be correct to assume that MFT is limited to these models only (either along with stock drivers, or as an additional install/redistributable, possibly depending on OS)?
Update 2: To quickly find out if H.264 encoder is available in form factor of MFT, one can use this app which enumerates hardware and transforms and produces a report. There will be "AMDh264Encoder" in the list if the MFT is available. The list also includes other (similar) encoders:
Update 3: Information that confirms availability of the MFT for specific products (goes in line with the link in Update 1 above):