If you’re flying in the US, there are downloadable charts (current ones - not from 2008) available from the FAA. I have several downloaded, and have the Airport Diagram for several favorites printed and kept in a binder (with freq’s printed on the backs) so that I can look them up without having to switch to a different program while flying.
https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dtpp/search/
In real life you wouldn’t carry out an ILS without reference to the current approach chart.
It lists the frequency, runway elevation, decision height, final approach fix and height, glide slope angle, rate of decent for your speed etc.
Using a chart in the sim is the most realistic way to ‘simulate’ real life IFR flying and is very challenging and satisfying. All of the USA charts are free with SkyVector, and much of the rest of the world are free via google etc.
I use Quick ILS. Just write ICAO code and get info about the runways, lenght, course, ILS frequency and elevation of the airport. https://flightsim.to/file/1629/quick-ils
Proper Prior Preparation Prevents P**s Poor Performance.
Generally speaking, prior to departure, (assuming I know my destination), I will reach into my flight bag and pull out my Jeppeson Binder, find the charts for my destination, review them and attach them to my chart clip.
In the sim, the real world equivelent is to download the Arrival/Approach Charts from SkyVector, Navigraph, LittleNavMap or whatever source you prefer and review them and have them available somewhere that you can quickly reference them when ATC actually gives you a clearance.
There is no substitute for a little preparation other than MORE preparation. 
I think this website is the best to find a ILS frequency
For europen charts you might want to have a look into the Eurocontrol AIP library. You will need an account, though. Wich is free for basic information.
EUROCONTROL - The European Organisation for the Safety of Air Navigation | EAD Basic
That data is 12 years old and very likely to have errors.
It’s a great question and as others have already said, I’d like to second them and say that I would look up the charts of the airports I’m flying to/from and gather that info before my flight.
Little Nav Maps is my in-flight reference if I need to divert to somewhere else unexpectedly. I guess this is similar to what one might need to do during a real flight using foreflight or something similar? Not being a pilot, I don’t know if that’s what can be done IRL.
I have also successfully managed to look up info in the Garmin Waypoint info options, though I found it fiddly with the mouse.