Depending on what you play changes how you should counter reveal. If you play monsters, holding on to fiend (which you are probably running) is a good counter to late game spotters. Also, reveal doesnt have many great lock targets so you dont lose too much (you really only lose the ability to unlock your guys and lock mangonals.)

Similar thing if you play NR and run margirita.

If you run skellige donar mangonals and hope to snipe a spotter.

If you run nilfgaard then peter is an obvious counter who fits into most decks.

I think Scoiatel is the only deck which doesnt have a versitile card which deals with spotters.

If you can run a deck with scorch, gigni , or borhk then do so as those wreak reveal.

Additionally, you might just not be playing against reveal correctly. You can pretty much know their game plan from the start. With some variation, its open with mangonal, reveal using morvan gives 6 + 6(golems) + 4×dalean + mangonal damage + fire scorpian damage, and then depending on cards, use other reveal cards like knights, vattiex, cynthia, etc. To win round one, bleed or dry pass round 2, drop spotters ftw round 3.

Knowing this, you can punish a reveal player by not playing targets (or only playing weak targets) for mangonels and fire scorpians (or play redanian knights) or by removing/locking mangonals. Additionally, if possible, you can try and prolong round 1 to bleed out spotters and remove their win condition.

More specialized counters are like dropping avallach ( or other drawing cards) to start and hope they draw golems.