You simply can't catch it yet, i'm pretty sure you or someone else asked and I said that. Regularly you caught it in that Safari-like thing after Goldenrod, but that competition is not active in this beta.
I have 2 suggestions for you:
1. Take a FR rom if you have one (I bet you do cause you play that game through IPS lol), and take your SAV file there (AKA, if your Liquid Crystal's sav is named 'liquidcrystal.sav', turn it into 'firered.sav' or w/e your FR rom is called).
Now either go catch it there or trade it from another FR save if you have one.
IMPORTANT: ONLY SAVE THE GAME, WHEN SWITCHING IT INTO FR OR BACK TO LC, IN A POKEMON CENTER IN KANTO, WHICH IS IN A FLYABLE CITY. Or else you won't be able to get out and it'll get messy. It might be messy anyways, but just get out of the door and get back in.
2. Wait for beta 3, link confirmed you'd be able to trade there anyways, and I bet he'll implement the competition there so you could catch it anyways.
Edit:
Link, I also have a question to you for you, if you don't mind I ask - how long will beta 3 go for, in terms of the cities/gyms in Orange?