The sites below are reputable tube dealers that I have used in the past. I have never heard any Japanese tubes of which Matsushita is one, but the more sought after 6DJ8's are from Amperex (Holland), Telefunken or Siemens(Germany), and Mullard (England). There are others as well. The 6DJ8 is fairly inexpensive and plentiful when compared to the premium version which is the 6922 and the 7308. I think with $100, you will be able to purchase some very good 6DJ8's. BTW, Phillips is a pretty good tube.
http://thetubestore.com/
http://www.tubedepot.com/
http://www.upscaleaudio.com/6DJ869227308_c_42.html
http://thetubestore.com/
http://www.tubedepot.com/
http://www.upscaleaudio.com/6DJ869227308_c_42.html