Where is sola scriptura in scripture?

1. A Catholic apologetic trope is to ask where is the evidence for sola scriptura in Scripture. But that's like asking where's the evidence for the Inter-Testamental period in Scripture. Or where's the empirical evidence for the nonexistence of life on Jupiter.

Depending on the nature of the claim, positive evidence isn't the only type of evidence. Sometimes negative evidence is the kind of evidence you'd expect if the claim is true. There's no record of the Inter-Testamental period in Scripture since, by definition, no Scripture was written during the interval in question. If no Scripture was written between the OT and the NT, that lacuna is in itself evidence. 

Sola scriptura is a second-order claim. The first-order claim is about the primacy of divine revelation in Christian theology and ethics. In principle and practice, divine revelation can be oral as well as written. But that distinction is time-sensitive. The second-order claim (sola scriptura) denies that public revelation is found outside of Scripture after God ceased to disclose himself orally or textually to and for believers in general. There is no ongoing revelation in that sense (which doesn't necessarily rule out private topical revelation).

That doesn't require positive evidence, any more than the nonexistence of life on Jupiter can only be justified by pointing to positive evidence. Indeed that's a nonsensical demand. If something never existed, then there will be no record of it ever existing. That's probative. That's evidence. 

2. This also goes to the burden of proof. Should we expect the Bible to announce the termination of public revelation if in fact that's ended? Or should we expect the Bible to anounce the continuation of public revelation if in fact that hasn't ended? 

It's striking that in the postexilic writings there's no formal declaration of a hiatus in canonical prophecy. It simply lapses. There's nothing more that has to be revealed at that juncture. What was needed weren't more oracles, but some fulfillments. Revelation will resume when messiah comes. 

So that provides precedent for a sola scriptura principle. Yet the post-exilic writings don't alert Jews to the suspension of public revelation until messiah comes. It simply terminates as a matter of fact. 

To be sure, some sects and individuals try to fill the gap (e.g. 1 Enoch), just as apocrypha and pseudepigrapha sprang up after the NT. So that's another parallel. 

Christians are in a situation analogous to Inter-Testamental Jews. What is needed now are not more oracles but definitive fulfillments, when messiah returns. If Jews weren't alerted to the the abeyance of public revelation during the Inter-Testamental period, there's no expectation that Christians will be alerted to the abeyance of public revelation during the inter-Adventual period. Just as there was no public revelation outside of Scripture during the Inter-Testamental period, there's no public revelation outside of Scripture during the inter-Adventual period. 

3. Also, as a practical matter, it's not clear how advance notice would work. After all, a false prophet could always claim that revelation ends with him. It doesn't end before him. Rather, there's no more revelation after he passes from the scene. The mere statement in writing, in a document purporting to be scripture or prophecy, can't settle the issue. Instead, that would only push it back a step by raising questions about the authenticity of the writing or the divine commission of the reputed prophet. Sometimes we must take our cue from events rather than words. Some things stop happening.