Just looking again at your photo, there appears to be a plastic beading which are often inside the unit, if this is the case it might be difficult to source an exact match. It was law between certain years for the manufacturer to print their name on the glazing bar, the silver aluminium part which seperates the two panes. If you can find who this was then you stand a chance of an exact repacement, however if you can find this you should hurry as styles change very often. It might be the case the window has to be opened up so you can retreive the beading, which will mean being without glass in the frame for a time.