Bubble gasket is the seal between the opening sash and the window frame, the seal that fits between the glass and the frame is called "wedge gasket". Copy and paste this link into your browser and save yourself lots of cash. No, I don't work for this company......*
Ex-window fitter just looked at my windows, said I need to replace mine. Sounds like you're looking for something called 'bubble gasket'. Google it and you'll find loads on internet.
A, June 2009
Some double glazing fitters will sell you this seal, others won't as they like to charge you loads of money to fit it, phone around first. Take a piece of the seal with you, there are a few different sizes.