Had to go with ABS black plastic t's on the 650C carbs I just rebuilt. I found them at Ace and they cost $1.70 each. I had to rip the old rubber ones off of the aluminum tube and sand off the glue. The ID was a little small so I drilled them out just enough so they fit tight. I had to cut some length off to make them fit between the carbs as well. They really only vent the float bowls but given the trouble I read about with cb650's having acceleration problems related to these vents I figured they were worth the trouble to hook back up. The original ones list for about $45.00 each on my local dealers on line parts fish so I didn't even try to see if they are still in stock.
