nuvistors for Musical Fidelity NuVista CD player

I'm seeking a parts source for the nuvistor output tubes used in the Musical Fidelity NuVista CD player (seller does not have the manufacturer-supplied spare set of nuvistors). I do not have the actual tube numbers right now. M.F. support is somewhat backed up lately and I need this info. in a timely manner prior to finalizing sale.
Does anyone have the *nuvistor* part numbers for the NuVista 3DCD player (not the musical fidelity part#)?
Who is a parts source for these nuvistors? I tried the [tubes-experts] Upscale Audio (original selling M.F. dlr.) who refers back to Signalpath in Charlotte N.C.
Surely some other expert tube sellers whould be able to assist - any suggestions?
thank you - Bob B
I could be wrong, but I thought nuvistors were only available from Musical Fidelity. I thought they kept a certain number around for repairs, and nothing else.
I'm pretty sure that MF held back a backup pair for each unit produced and the US importer or manufacturer should be able to help with procuring them. I would be surprised that they would be needed anytime soon though, I thought the life span was in the tens of thousands of hours? Also I'm pretty sure you can sometimes find folks selling nuvistors on Ebay, perhaps NOS backups could be procured more easily there? Good luck!
Researching my hardcopy archives I believe you're correct; they issued certificates along with each player qualifying original owners for a replacement nuvistor pair. Thanks for your replies I'll keep trying Signalpath.
You want the 6CW4 nuvistor tubes. Other than Signal Path you can buy them from the following tube stores.