if you cant find exact bungs just get bigger ones and cut them to size, and definitely dont throw all that good mead out just distill it like fatbloke suggested,honey alcohol is yummy
I would run some of the liquid through a screen and then through a water filter. Then see how it tastes. It may make a great vinager or stock for curing sweet pickling or something. A good general rule of thumb, never toss mead. It can always be used for something, even reduced make a great sause starter. What do you think that soy sauce is. Fermented soybean juice. May not taste good on it's own but add it to steak and other meats and yum. Also boiling it should be a priority too to purify it if it has any nasties in it. Cooking with mead is great. Especially on pork. I had an undrinkable orange rosehip mead that was just too potent and hot in the fusel alcohols but it made a great pork roast marinade.
As Mr. Matrix suggests - many a horrible batch has been rescued with the application of the water filter.... You can strain out all sorts of horrible through one of those things.... Save the Vinegary ones for last....
As a few here have mentioned - varietal vinegars can be a lot of fun.... They can work well in cooking and salads...
What a shame it wasn't found in better condition. I'm not sure if concentrating it would be a good idea. I would think you'd just end up with all the tastes, including the bad tastes concentrated. I hope you figure something out... I'd hate to hear that it ALL goes to waste!