Have to say that you have pretty slim choices IF any.
My first xhoice would be LAND handhels pyrometer because of their top quality. Best they can offer is Cyclops 390L at 3.9 um. Less than ideal för glass.
Cant find anything from the usual suspects ie: LAND, ircon, lumasense, optris, heitronics, Williamson so i am affraid you got the shortest straw this time.
Some of the non-portable models are somewhat usable IF you strap external battery Back to them. LAND has a few 5um models and so does lumasense.
Id say your best candidates are lumasense in140 with integrated display or in5 with external rs232/4-20ma connected display. Both will need external battery pack and possibly some sort of pistol grip för handheld use. You are probably better of with laser aiming than see-through optics.