All ICAO countries (that is national states) produce their own airways charts relative to the country and airspace they manage. There is not to my knowledge a single world wide type chart but buried on the US FAA site is a link to some charts produced in large scale which effectively cover about half the globe, they are in PDF format and when you zoom them up they are fine for routes airports and navaids, they are of a size that was mean to go on a large overhead display or wall so they are very big.

Otherwise country by country, some publish airways charts that you can get for free others you have to pay for airways type charts. The suggestions abobe are all good ones. I find I do it country by country and where I have to pay to get a chart I see if I have a friend who has one or they have been posted at some of the various sim websites catering for virtual airlines as well.