Silly new to the east coast question

No fewer than one and a half dozen... And that was even without Jenna and her bow floating around!

Jenna doesn't need her bow for groin shots. I know this for fact.  :'(

As for the OP... Amazon.com, Patagonia, Under Armour... the list goes on.  I won't endorse any 1 brand.  Instead I will ask that you pack a few changes of long underwear/thermals/whatever you use. When larping, I have found I will go through a few changes of these due to sweating during fighting, & then freezing while waiting in ambush or while guarding folks.  Warm, clean, DRY layers are key during winter larping.

It's October and we already have this happening.  When you come during December, it could be nicer, or it could be much worse.  Play it safe.

Edit: added link.

Jenna doesn't need her bow for groin shots. I know this for fact.  :'(

You know, its not *my* fault my swing zone perfectly coincides with your groin level: I'm a midget, and you're all 8' tall pituitary freaks.

OP, don't forget plenty of blankets and a warm sleeping bag. If you don't have a sleeping bag at all yet, I recommend splurging the extra few bucks for the ones that are rated for below freezing temperatures. Even though most of the buildings are heated in winter, you're going to be glad you have one on those spring and "summer" nights when we sleep in the tents and the temperature decides its going to drop down from 98 to 35.

thread officially derailed...

You know, its not *my* fault my swing zone perfectly coincides with your groin level: I'm a midget, and you're all 8' tall pituitary freaks.

Did you just call me a 8' tall pituitary freak? Seriously?  How many Big & Talls do you see in China? 

...its ok Paul, when Jenna hits you in the groin, just call BACKPACK for a defense.

I have not heard the words Silk or Wool mentioned as layers for regulating temperatures

 I teach the BSA youths during Klondike Derbies  that "Cotton Kills"  

Cotton should be avoided at all costs during cool/cold weather as we all sweat with heavy activity and cotton holds in the moisture  and rapidly cools the body down starting the Hypothermic symptom of shivering, then can progress into serious trouble

Check the Good Will and Salvation Army or other thrift stores for used sleeping bags  wool sweaters  
Visiting the thrift stores is a little like playing the Lotto  . Sometimes you win, Sometimes you don't

I have found many useful cold weather gear items at thrift stores

Layers of wool and silk are the key with some method of opening/closing the front to vent and regulate body temp  Also wear a hat

I too really like the HalfMoon stuff

Silk underwear can be bought at Cabelas or Bass Pro