The Rainbow Fountain is a decorative item in the Neopets world and doesn't have any function related to getting paintbrushes.
There are a few ways to get paintbrushes in Neopets, including:
* Buying them from the Neopets Shop: You can purchase paintbrushes from the Neopets Shop using Neopoints.
* Winning them from games: Some Neopets games award paintbrushes as prizes.
* Trading with other players: You can trade for paintbrushes with other Neopets users.
Let me know if you have any other questions about Neopets!