Google Play Store Free Coins
Didn't see it listed or mentioned but you can find a few links a week in the reviews. Check under the House of Fun reviews, and sort by most recent. You'll notice responses by the developers with a link attached. These when successful reward more than any other links I run across. Found one today for 14m (lvl 1140), generally getting either 1.3-1.6m or 4.3m per link.
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