I get everything for mine from Fallons Home and Hearth in Hampton, NH.  They are fantastic, always go above and beyond and are priced more than reasonably if not the best price.  Know they are one of the largest Harmon Dealers in the area as well from what I've been told.      
http://fallonshomeandhearth.com/ 
Side advice based on experience:  Have a Harmon pellet stove downstairs.  Decided to do a gas insert in the fireplace upstairs (best decision I ever made in my opinion).  With propane prices (I'm paying around $2.00 / gallon) it ends up being cheaper than pellets (I burn Vermont Pellets).  First year I owned this house (3 years ago), I heated the entire house, both floors from one pellet stove on floor 1.  On really cold days, the second floor was about 60 which is a bit colder than we like.  We got the propane insert, keep the house at 70 and iv'e probably spent this entire season $900 on propane and gone through 75% of a pallet.
We travel often, so pellets dont' work well as our hopper taxes a little over a bag.  With the wireless thermostat for insert, we leave and know we are golden.  
Best thing is no cleaning, lugging pellets, and the typical maintenance needed with a pellet stove.  
If you have Natural Gas, even cheaper than propane so it's a no-brainer in my opinion.