@Tom Bavis says the 6F2 is at least similar to the 6U8 and (thus) 6GH8.
https://www.audioasylum.com/cgi/vt.mpl?f=tubes&m=240800&VT=T
These tubes are a medium mu triode and a sharp-cutoff pentode in a single envelope.
http://www.tubebooks.org/tubedata/HB-3/Receiving-Type_Industrial_Tubes/6678_6U8-A.PDF
Whether ia 6U8 or its kin is utterly and universally interchangable with the 6F2, I dunno.
6F2 is not listed at TDSL
http://tdsl.duncanamps.com/tubesearch.php nor is it mentioned at Brent Jessee's site
http://www.audiotubes.com/chinese.htm
The big question (in terms of sourcing a substitute or workaround for the 6F2) will be whether one or both sections are used in the circuit. If only one section is used, which? In any case, what are the operating points? I'd also check the filament current draw of the 6F2
vs. the 6U8 (to make sure the filament supply isn't going to be overburdened).
If a 6U8 (etc.) works in the circuit, great. If not, it might be possible to revise the circuit and/or "just" to rewire the socket to use a different tube. Actually, it should be possible
but it might not be worth the effort!