You've got to remember, all these top gaming youtubers more or less started during the boom of it and have also been going since 2010 -2012 so they've had 4 or more years to build their fan base and amass the funds to pay for all these new games/hardware that are coming out to keep their subscribers happy.
As for the clips your wanting, Are you wanting shout outs on other peoples channels? If that's the case, try contacting certain youtube channels that do shout outs, see if there is something you can do for them to get a shout out.
If your wanting clips from other youtubers to get a shout out on their channel, again contact them, ask if its OK to download their videos from youtube to make a shout out, most will probably say yes as its extra promotion for their videos.