Like others have said, I wouldn't have patience with a tube amp that demanded NOS tubes to sound good. There are plenty of good new tubes on the market today. My Williamson amps sound great with Gold Lion KT66's and GZ34s, and Tung-Sol 6SN7s.
Would you buy a tube amp if you were unable to use vintage tubes in it ?
Not available or too expensive.
Hmm.., I don't think I have a definitive answer for myself, but I would do my best to avoid such amps. There is no substitute for great tubes, I guess, especially if you value sophisticated sound.