How do I connect a portable gas generator to the house?

Where can I purchase a portable generator transfer switch?

I separated your questions from the old posts you began with, and then merged the two questions into one thread.

Not sure if this site has what your looking for:

Gentran Corporation: Generator Transfer switches for home & business

You may need to buy a standard transfer switch and make it portable.

As far as your connection to house question, get back with more details.

One of the Cheapest, fastest, most effective ways is with a interlockkit. (Generator InterLock Kit).
It allows only the Main breaker OR the top right breaker(generator breaker) to be on at a time, prevents back feeding.
Many places sell a transfer panel that allows 10 circuits(more or less) that can select between Electric Company or Generator, and only those selected circuits.
The Interlockkit allows Any circuit in the panel to be on, limited by the generator output.
I turn on all 120 volt circuits, and turn lights on and off as needed. You only have so much power for small setups. Above site is good, I also like:
http://www.electricgeneratorsdirect.com/