Snake Eyes Gaming,
http://www.snakeyesgaming.blogspot.com, runs events in Pennsylvania. While our events don't quite make it out to Lancaster I can tell you that we run exactly the type of thing you're looking for. We almost always have a table set up for beginners and the players that come to our events generally seem to really enjoy themselves. The most convenient locations to Lancaster would be the Toy Soldier Gallery in Ligonier or Gatehouse Games in Altoona. We have upcoming Mixed Doubles events at both. Basically, you bring 1000 points and each round you are randomly paired with someone else to play against another pair. These events are incredibly fun and provide a good chance to meet new players.
The players that show up to our events come from central and western Pennsylvania as well as northern Maryland. We have had several players come to events from the Philadelphia area. Feel free to
PM me if you have any specific questions. I hope that one of our upcoming events is close enough that you can make it.
By the way, about half of our events are FREE. Games Workshop generously provides us the prize support that we award.