Probably going to have to be a two part epoxy. Check the packages at your local hardware store. The optical guys use a two part epoxy for glass to metal bonding, but the stuff they use will be scary expensive for you (the minimum order is probably more than your lamp is worth).

The problem is going to be the heat from the light.

Heat will weaken even epoxies (and MANY other glues) long term).

At least do a search for 'high temperature glue' and see what you can order.

There ARE epoxies rated for higher temperatures.
Ceramic based adhesives are more common for this application.

You may be able to find someone who selling single tubes/containers.

Is the metal to glass bond holding the weight of the glass?

A lot is going to depend on the size/weight of the glass. If it is small and light a hi-temp silicone may work also.

Loctite 349 Impruv Light Cure Adhesive

Just home from work. You guys are the best! Retail on the fixture is $239 and that would be my cost to replace it. Brick, I remember you from years ago!