The 21-year-old was previously with Cypriot club Onisilos Sotira, and his move to the League Two side is subject to international clearance.
"Alistair is a young player with a hunger and desire to make the most of the opportunity we have offered him," said boss Ian Sampson.
"We are happy to take a bit of a chance with him."
Slowe played youth football for his hometown club, Brighton & Hove Albion, but moved to Ghana in 2006.
He played for Cantonments for two seasons before switching to Cyprus.
"He is not the finished article yet but he has potential and good technical ability," added Sampson.
"He gives us something in an area where we were looking to add and is a welcome addition.
"Because he has been abroad he has slipped under the radar a little."
Source: BBC Sport
Source: BBC Sport