Judging by the photo, there looks to be a small crack in the bottom right lobed panel, also there are three tiny triangular glass pieces that are painted over, which could be an indication that they have been replaced with a piece of thin board or sheet metal. From outward appearances it looks to be in fairly good condition.
If this is all that is wrong, then it should be fairly simple to make some templates and have the glass cut. this will be thinner than normal, and hand blown. Ones best bet at getting this done would be a a stained glass place.
I would agree with others about not using heat to soften the putty, best stick to a strong commercially available paint stripper, that will also do the job. In short, if my guess is correct, the repair should be quite simple to undertake.
Ooops! just seen the last post............... In light of this I would try contacting some of the larger architectural salvage firms in the area. They often have associations with firms who repair and supply reproductions of the items they sell.