Hello:

Is there a gas boiler and electric generator combination for home use?

excon

Sort of. Google "micro-cogeneration". Though not a boiler this may interest you. A gas powered engine spins a generator for electricity and the water used to cool it provides heat and hot water.

Cannot seem to find a commerciallly marketed product.

Fairly simple thou, need a steam boiler and a steam driven electric generator.

Here is a link to someone that has a package put together, seems most are home grown systems,

The Liberty Man - Steam Generator