According to 'Mistel', by Hans-Peter Dabrowski, the Führungsmistel was projected only, never built.
I have only one photo of an Fw 190A-8 with the 300 l. Doppelreiter tanks, Weisses 7, W.nr. illegible (in shadow). Hakenkreuz is in earlier style associated more the A-3/4/5 however, which makes me wonder if it wasn't a test aircraft.
I don't believe I have ever seen a photo of operational Misteln showing Fw 190 führungsflugzeuge with the Doppelreiter tanks.
Of the more than 200 Misteln built, not that many were actually used operationally in any case, often through plain bad luck (lead aircraft blowing tyres and blocking the runway preventing the rest taking off, for example). Shortage of fuel and Allied bombing put paid to many aswell.
Will read that book again, though I don't recall specific combinations being mentioned in the operational histories, only the unit. One photo caption states however:
'Ju 88H-2: approximately 10-12 examples were built, most of them planned for Mistel operations'.
That makes me wonder if any H-2s were actually fitted with a warhead at all, or just 'planned' to be so... certainly all published photos I have seen are of S-3C Schulmisteln only - though of course that by no means rules out the possibility that some may in fact have become operational 3-C Misteln.