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If your current requirement is below, say, 200mA, try charge-pump dc-dc converters .
I assume you already have 0-to-(+V) supply, so you just need to add negative rail ..
Theses charge-pump converters will produce 0-to-(-Vin), in some cases (-Vin) and/or (2Vin) ..
Here are examples:
and so on ..