I've found almond flour everywhere but I'm allergic to almonds...
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I Googled it and came up with this. It looks promising. Hope it helps.
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Can you sub hazelnut flour? I've seen that a little more frequently (Bob's Red Mill makes it, among others I'm sure).
Alternatively, you might try making walnut flour in a food processor. Be careful that it doesn't turn into walnut butter/paste by pulsing and keeping a close eye on it.
I have seen pecan flour at the Gordon Food Service Store.