There are a few paths to securing sound effects for an opera production. The simplest approach is to find existing sounds online or via sound effects libraries. Another option if you need something that isn’t readily available is to record your own sound effects which is both rewarding and allows for the possibility of creating something that is catered specifically for the productions needs. I’ve recorded a helicopter before because what the director had in mind didn’t exist. It turned out great. No amount of trying to use existing helicopter sounds would of created a convincing effect. In order to record your own sound effects you need some sort of recording hardware which could be as simple as using your phone or as complicated as using a multitrack system with multiple mics. The BBC has produced the largest publicly available sound effects library I’m aware of. Here is a link to their collection. http://bbcsfx.acropolis.org.uk/

Another resource is John Leonard who may maintain the largest private collection of sound effects in the world. https://www.johnleonard.co.uk/

I’ve sourced multiple sound effects for opera productions through John. He is routinely on location wearing a set of headphones so don’t wait until the last second to ask about sound files.