Where is professor oaks aid that gives you the itemfinder in firered?

You get the Itemfinder from Professor Oak's aide, not Professor Oak himself, in the Pokemon Center of Viridian City.

Here's how to get it:

1. Talk to the aide: You'll find the aide standing to the left of the counter in the Viridian City Pokemon Center.

2. Receive the Itemfinder: They will give you the Itemfinder after a brief conversation.

The Itemfinder is a very helpful tool for finding hidden items on the map. It's a great way to find rare items and boost your chances of catching wild Pokemon!