Vacuum Tubes for Leben cs 600


Has anyone tried replace the 6CS7 and 6CM3 tubes in the Leben CS600.   I understand the genesis for the CX600 was the shrinking availability of valves and tubes for the cs 600.  As such I thought might be worthwhile stocking up with spares for future replacement.  Well, there are not many out there.  Has anyone had luck locating these tubes?
Thanks,
MP
rivinyl
I'd start with the USA importer if you are in the USA, next I'd contact a few premium tube resellers. A quick look on the web showed many choices. 
This is confusing and comes up on the Facebook site occasionally. I spoke with the Japanese exporter and he claims the amp can be upgraded to the X version. The importer says it can’t be done. 
In any event I have some tubes left from when I owned this amp. A matched quad and a half dozen NOS tubes. Let me know if you have trouble finding them.