Since when do we do that for police searches for crimes in progress?
Drug dealers are notified that the police are seeking a warrant on their address and given a chance to review the evidence?
There is no adversarial process in getting the warrant, but the people on whom the warrant is served are given a document explaining the evidence that led to the warrant. The police give it to you when they do their search, or after the search is complete if it was something like a wiretap.
If the document does not support the need for a search or contains evidence that is fraudulently obtained, you can fight it either by striking the evidence at your trial or by separately suing the bad actor. At a minimum, during your trial, the warrant becomes part of the record and is publicly obtainable.
In the FISA case, the warrant document does not contain the evidence against you, since it is secret, barring you from fighting its validity later.
Also, when a crime is in progress, police don't need a warrant if they see it. They can just intervene. However, they can't search you for evidence of further crimes without probable cause of that other crime or a warrant.
Anyway, separately from that, what is your position on the statement that for certain types of evidence and cases in progress, the accused should not be allowed to see the specific evidence (and methods of collection used) against them, because it would compromise compelling national security considerations?
How about if it were to be unsealed after some amount of time when the need for security of the collection mechanism(s) were to have expired?
There are no legitimate "national security considerations" if you're going to use that information to try to take away someone's rights. Their security from the nation outweighs the supposed security of the nation against any supposed adversary that might use that information against the US. If they want to use any information to get a warrant, the relevant investigator would have to narrow the evidence they use in court to what is okay to reveal - they do that anyway on normal warrants. Also, why would there be national security considerations on evidence against particular individuals anyway?
Finally, waiting until unsealing to allow someone to fight a warrant would take too long. Documents tend to take over 20 years to be unsealed, which would mean that an innocent person could sit in prison for their entire adult life while waiting to fight an illegally obtained warrant. No.
If the search turns up evidence, and the government wants to use that evidence at trial, then the affidavit is available in discovery.
If no trial results, I don't think there's any reliable way to get at the affidavit.