It's a bit misleading to think the UN only has “limited” peacekeeping ressources. The reality is that it does not have any military force that could be freely dispatched anywhere in the world under UN command (that may have been the original intent but it never happened). Instead, the way UN peacekeeping works is that countries provide troops for specific missions (they get money for this).
On the other hand, if you include all soldiers currently deployed for the UN, the total size of peacekeeping operations is actually quite large (currently over 100 000 personnel) and growing. And its only limited by UN member states willingness to provide ressources and funding for a mission so that, if UN security council members really wanted to create a new one, they could probably find the ressources too.
Another model is for some countries to deploy forces directly to enforce some UN resolution but without formally belonging to a UN peacekeeping operation (that also means no blue helmet and a different chain of command). In particular, the US does not provide significant forces to the UN (they do provide a lot of funding). Enforcing a no-fly zone requires very specific capabilities and I think it has always been done directly by a handful of countries (US, UK, and other NATO members).