Yes, deponent verbs have gerundives, and these are passive in sense.
For the OP's benefit:
numquam obliviscendus means "never to be forgotten", referring to one male person;
numquam obliviscendi means the same referring to several people either male or both male and female. (Perhaps this was already said in one of the links provided by Etaoin, which I was too lazy to look at, but even if it was, I figured it wouldn't do much harm to repeat it anyway.)
Otherwise, I confirm Imperfacundus's translations of "never forgotten" (if the sense is "having never been forgotten") and "never forget". However, if the latter were a command to a female, you'd need
oblita instead of
oblitus.
Google it's translating
numquam obliviscar
to: I shall never forget.
For once, Google is correct.