Use Tiny Umbrella (TU) on your old PC to find the files...
Start TU on your PC. Go to the Advanced tab and find the line "Save SHSH Directory." That's where TU put your SHSH blobs - so navigate there and copy the files. Note that all the SHSH you have should be in a folder (that's very high in the hierarchy) titled ".shsh"
Copy the whole folder and put it wherever you choose on your new Mac Mini. Just don't forget where you put them!