All the "your gear is high enough" posters assume the OP is running at cadences similar to theirs. But cadence varies tremendously among riders, so the OPs request may be very valid - for him.
I agree that the only readily available mechanical option are larger chainrings. However Moulton used to offer hubs and freewheels with sprockets smaller than 11, though I don't know what the smallest was.
The downside is that it would require a new hub so change.
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