
I've found these two sources to be outstanding based on both quality and quantity of available free books.
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mod: first link contains unauthorised copyright material. Please do not link to it.]
http://freeread.com.au/ (Roy Glashan's Library)
My only regret is not finding any of the Maxwell Grant Shadow novels. I've listened to most of the extant radio episodes. Of the 700 Shadow episodes only 200 +- are known to exist. Sigh

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