The exact model doesn't matter as all Smith-Corona Super-5 variants used the same typewriter ribbon, which means any common typewriter ribbon (½ in./13 mm) will work. You can get the platen refurbished, but it's not cheap. Why do you think it needs to be replaced, because in your photo it looks to be in good condition. 

Based on its feature set the "Enterprise"  it's very similar to the Clipper, which has two additional keys in direct comparison. 
 

theinforat wrote:

It's either the platen or the rollers underneath. It doesn't pull the paper at all. 

Much more likely to be the feed rollers, or an issue with the paper release mechanism. I assume you DO have it in the correct position to feed paper?

theinforat wrote:

I am a bit curious about it's age though.

Is there a letter in front of the 5A in the serial number? The A in Smith-Corona numbers typically indicates a Sterling model, however, all Super-5 machines like yours were produced between the late 1940s and early 1960s. 
 

I went to this website and just followed the design changes based on images.

http://sevenels.net/typewriters/s-coronas.htm

There are small changes that happen in each of them, and this seem to fall between 1956 and 1959. I am an amatuer, but that is what the images suggest. I would be curious to learn more if you ever get an answer. I was intrigued to learn that in Europe there are names that are not seen here in the US. I like Royals, and just learned about the Administrator and the Diane. I kept thinking that the Diane was a fake.