Also, you might try the Historic Joist Catalog from the Steel Joist Institute. I don't know if it lists by manufacturer, but it might help you out.
Do you know the date of manufacture? If so, in addition to waht fepc says above (which I have done many times myself), you could figure out the weight in lbs/ft. Then from a load chart (like in historic catalog) you could cross reference your calcs to a published value. Just make sure you correct for allowable stress.