Call Andy at Vintage Tube Services and see what he has in stock. The $70 Matsushita made in the Mullard tooled factory in Japan will get you about 95% to the Blackburn factory Mullards for about half to a third of the cost and will likely outlast you. Though you can find them badged Matsushita most were made under OEM contract and branded as Dynaco, Westinghouse, Baldwin, etc. Trying to buy 5AR4's on Ebay could be an expensive waste of time.