If we are being exactly correct, it should always be "there ARE two of something."
However, in spoken English, you may hear "There's two ...."
You will always hear it as a contraction - almost never as "there is two...". It is an error, but it ends up being said a lot in everyday spoken English. If you say it, I doubt anyone would correct you.
It's better to use the correct form, though.
"There's two guys outside waiting for you." [Correct: There are two guys...]
"There's four cars parked in the driveway." [Correct: There are four cars...]