That's a tough one. It can be very difficult at times to come into the US on a Visa. There are a lot of factors, prime among them being how many visas the government is willing to allow and whether or not the studio you are applying to can afford a lawyer to get the visa situated for you.
However, one thing I know can help you get a job here: Awards.
If you are an award winning animator, recognized by institutions or film festivals or what have you -- these awards can make it much easier for the studio to argue your case and get you that visa. The way things work here is that if a studio wants to bring you to the US, the lawyers have to draw up the papers, apply for your visa, etc. There are application fees, lawyer fees, etc. This amounts to thousands of dollars. (I heard $7500 once, but I don't know how accurate that is). This money is NON-REFUNDABLE, so a studio, particularly any smaller studios, can't take the chance on an iffy visa application. If the visa is denied, they lose their money AND lose the artist they were hoping for.
However, if you have won awards through your work or through film festivals, be sure to let the studios know, because it increases your chances of getting a visa, which increases the chances that the studio will be willing to gamble on getting you that visa! Make sense?
So, my advice for international students who want to work in the US is this -- make a short film, make it amazing, get it into festivals, and win yourself some awards!
I know that's a tall order, and it might even sound impossible, but you know what? Someone is going to get their film into that festival. Someone is going to win an award. Someone is going to get their dream job.
Why can't it be you?