If you're ok with using a parabolic mirror(s) as the heat source instead, then it should be doable. eg:

http://web.archive.org/web/20060508061432/http://solstice.cr...

They specifically mention systems that do 5kw, 25kw, etc (in the next pages).

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That aside, there's a kickstarter project for a 1kw Stirling engine from about 6 years ago:

https://www.kickstarter.com/projects/672465444/low-cost-ster...

The "updates" tab there seems to have potentially useful info, though the project appears to have stopped updating there.

The project itself still seems to be iterating on new developments, just slowly.

http://volodesigns-sterlingproject.blogspot.com/

More recent video's of their development:

https://www.youtube.com/watch?v=p06HDOlxDMM

Mentions here they're intending on making the design OSS:

https://www.youtube.com/watch?v=IrXltsm-Ujs