Rocc - I'm very happy with Mullards in my premier 14 over stock GE and Sylvania. Try Upscale audio, at the very least you should have different types of tubes to experiment with. I was using stock for a while and switched speaker cables from Kimber 8TC to Alpha-Gore MI2's and the stock tubes sounded a little aggressive on the top end, especially on bright digital recordings. The Mullard's in this case are a better match, much less fatiguing, instruments sound more life like IMO....
Best cheap NOS tubes:GE, Phillips and Sylvania
LIVING IN CANADA AND NEED TO RETUBE MY CJ PREMIER TEN WITH 6GK5 GE,THEY ASK A LOT OF $$$.SO WHERE I COULD MANAGE TO HAVE A GOOD CHOICE OF GE,PHILLIPS AND SYLVANIA TUBES AT A GOOD PRICE?