Double-hung window sash glass replacement

Double-hung window sash glass replacement - Looking for window expert!

The house is in Rhode Island, east coast of the US.

Last night was a really windy night. My bedroom (on the 2nd floor) has a double double-hung window and one of the sash's glass got blown away, fell, and broken. I saved the trim pieces and surprisingly noticed that there was no staples or glazing compound on the sash frame to prevent the glass from flying outwards. The only thing that was supposed to hold the glass in place are four pieces of vinyl/plastic trims that was jammed into place.

The cheapest solution seems to be sash glass replacement at the moment. The measurement of the glass is 20.5in (width) x 28.5in (height) x 0.484in (thickness) and it's a double-pane glass with metal spacers in between which has a stamped label "multipane--- 692" on it.

The problem is the sash removal, the window balancing mechanism doesn't seem like anything I've been watch on the videos online. Instead of using pulley-cord counter weight, each sash has two springs hidden (but still visible in the photos) in the track cavities on each side. There is no cord or clips that helps me to dismount the sash without breaking the trim/stop board.

If it's possible to put the replacement glass onto the sash without removing the sash first I'd go for it but being on the 2nd floor I really think it's better to remove the sash first.

All the photos for reference are here:
http://s963.photobucket.com/albums/ae118/lancey2010/window/

recap:
1. where can I find this multipane 692 glass?
2. how to remove the sash with spring balance?

Photos:
1. The glass of the upper (outer) sash is missing:



2. There are no visible cords/pulley for weight balance for the sash because it uses spring on each side and the spring is located in the groove next to the track


3. This is the close-up photo of the spring. There are no tabs or stop piece on the sash or the spring track so I can't figure how to remove the sash without take the whole thing apart (which I really don't want to do - but sash removal seems essential to put the replacement glass in).
More photos in http://s963.photobucket.com/albums/ae118/lancey2010/window/