You are never going to find exact copies of Vegas slot machines online due to copyright issues.  Most of the machines you are familiar with like Little Green Men are built in the US.  Thanks to oppressive gambling restrictions American businesses are not allowed to run online casinos, and therefore US slot machines are not going to appear online.

If we eventually get a government that believes in doing what the people want, rather than simply pushing their own agenda, we could get a taxed and regulated online gambling industry here in the US.  When that happens all the casino favorites will likely end up online.  Until then, the best you are going to get is a poor rip off of the real life machine.