Right now the elderberry bushes are flowering. Look for them in marshy, sunny places. There are a lot of plants out there that have white flowers, so make sure you identify the leaves and flowers correctly. Wildman Steve Brill is always a good place to start. Identify plants while they are flowering, even if you're not going to make elderflower cordial or elderflower liqueur. That way when the berries start to ripen you will already know where to look, and beat the birds. Or me!
I made elderflower liqueur last year, and it's not quite St. Germain. It's very woody and herbal. I think this year, I'll just wait for the berries.