I think it's from a set of replicas of historic medals that the US mint put out in the mid 70s. If you look on eBay you can find the whole set. It's very cheap to get. And yes, it's pewter.
In a weird way I kind of like these pewter medals, if nothing else for the fact that they are made out of pewter. When was the last time the mint released anything in pewter? As far as I'm aware it's been a long time. In fact, this set from the 70s is the only time they've done it. Correct me if I'm wrong.
http://www.ebay.com/itm/252515787758 $1 plus shipping ($1.75) in OGP. Set of 11 seems to have an Ask around $25.