PCAP files for use with Eye P.A. can be obtained from several sources.
Windows: RiverBed AirPcap Nx
The AirPcap Nx is a USB wireless packet capture device (802.11a/b/g/n 2x2 MIMO) that overcomes the typical wireless packet capture limitations of Windows. Support for this device is built-into Eye P.A..
macOS: Wireless Diagnostics Tool
The Wireless Diagnostics Tool in macOS makes wireless packet capture very easy. When you are done, you can move the WCAP file into your Windows virtual machine by dragging and dropping the file.
You can also use Dropbox or BitTorrent Sync to move the file to a Windows machine for analysis.
Linux: Normal WiFi Adapter in Monitor Mode
Common Linux tools like airmon-ng and tcpdump can be used to generate PCAP files. Just be sure that your wireless adapter can be put into monitor mode.
Network: Enterprise-Grade AP
Some enterprise-grade AP's can generate PCAP files. This can be useful for getting the AP's perspective.