How to Find ADC Converter

Well...

in fact there are many chips communicating via SPI I/F with different input signal ranges, resolutions, number of channels,... "on the market".

So far you did not specify which type of sensor you want to connect (or best which kind of analog signal (range, frequency, source impedance) you want to convert nor do we know which sample rate and bitwidth is required in your design...

If there is no high sampling rate required I'd go with cheap ADC of e.g. Microchip (e.g. the MCP3004), if you need higher sample rates, take a look at analog device.

At least any of these manufacturers have a "downselection" option, i.e. you can define the parameters you require and they suggest matching devices based on your requirements - this might be the best and easiest option...

That's just my humble opinion - there are many other ADC manufacturers (and I do not get money to suggest Microchip and Analog at all ... :) )

Regards