I want to start working with arduino/raspberry pi/esp32/sensors.
What would be a good source to buy these in bulk (along with accessory components. e.g. wires etc.)?
If you have a nearby hackerspace or similar, check it out.
Likely they will be able to help you choose and guide you.
For me the hurdle was less about finding equipment and more being able to learn from experienced people.
Take a look at adafruit and sparkfun
You can find kits that have a selection of sensors - enough to get started and experiment
https://www.adafruit.com/product/193