The filter is a standard 10" element; you can find them at Amazon, eBay, etc. Ensure you DO NOT get carbon filters - while great for drinking or brewing water, it's not so great for finished beer.
As to the adapters, you need two kegs (or at least one and a bucket or carboy, but watch for aeration), and associated fittings. Gravity does not provide enough force to push beer through a 5 micron or smaller filter. You use the keg and CO2 to put a few psi on it, and force it through.
You can pick up barb adapters for ball or pin lock kegs at your friendly LHBS, or internet mega-stores if not available locally. They're about $7.
In addition, most sites I've looked at recommend a two-stage filter setup, one 3-5 micron, and one 0.5-1 micron. At 0.5 microns, you're removing the majority of the yeast, and almost all haze causing proteins. At 1 micron, yeast remains, and you don't get as much haze out.