well you have a few options - you probably shouldn't have thrown that speaker out - you could have just taken it to be re-coned. It would be cheaper than a new speaker and it would be restored to the original factory specs.
I assume that this is a PA speaker and that you have another one that matches? If so, then you are going to want have a pretty closely matched pair as far as the wattage rating (RMS) and frequency response. If this is the case, then get the model # and manufacturer and do some searches - try USSPEAKER.com - they have lots of options. Also, try ebay - you might find the exact one.
If it's not a matched pair, then you can go with a variety of speakers as long as it is 8 ohms and at least 100 W RMS. A great speaker, and the one main 12" speaker that the dead used in the wall of sound as well as in speaker cabinets right up until the end - including jerry's 3 x 12 speaker cabinet - was the JBL E 120 - it is 8 watts (watch out though - there is a 16 watt version). It is a beautiful and powerful speaker - 300 W. That doesn't mean that it has to run at that wattage - it just means that it can handle it. A lot of people use them in guitar amps and pa speakers and monitors from 25 watts up. The speaker is not produced anymore but it is still a highly sought speaker because of it's brilliant quality. Look on ebay - there's almost always a few for sale.