Is there any External Graphics card available in the market which can be used with laptops via a USB port or EC slot on the laptop to increase its performance for playing games, etc.?
No Sire, no commercially viable design is available in the market. Which laptop do you have and what is its configuration?
Although there are reports of using Wi-Fi and its elder sibling WiMax to make wireless graphics cards.
Hope this helps, Cheers!!
Did a little bit of Google and this what it threw up, go to
this and this
link(s) for DIY set-ups.
Some more on the subject.
I still cannot guide you where all this paraphernalia can be acquired in the local [read Indian metros] computer component stores OR will you have to import this from abroad.
Hope this adds up. Cheers!!