Try these sites for tubes: thetubestore.com, upscaleaudio.com, tubesandmore.com, tubeworld.com (pricey but good for window shopping), jeffssoundvalues.com
Are your current tubes new? How old? The 12ax7 and similar will go for many years, the driver tubes will only last 1000-2000 hours and then will lose some inpact, clarity and control.
NICE SYSTEM though.