Browse the full line of Iwata compressors on the Iwata-Medea website. You can find a link to this site in the Resources section below. Although you cannot purchase a compressor from this site, it's a great place to start because it has up-to-date product information and extensive details on every available Iwata product. Conduct your initial research on this site to determine which compressor or compressors best fit your needs.
Conduct a separate search for each specific Iwata compressor model you're considering on a large shopping aggregator site like Amazon. You can find a link to Amazon in the Resources section below. This is the best way to get a huge range of prices at a glance, and it's entirely possible that you will find the best deal there, too. For now, just focus on the price ranges for each of the compressors you're thinking about buying so that you can eliminate possibilities that are outside of your price range.
Call the finer art supply stores in your area to see if they carry the models you're interested in. If they do, ask for prices and write them down. If they don't, ask if they'd be willing to special order the one you want and how much it would cost. Finally, be sure to ask about the return, replacement and warranty policies of each store. Every Iwata compressor comes with a one-year manufacturer's warranty, but it's worthwhile to see if extended warranties are available through the seller.
Search for your chosen models on art supply websites. Some links can be found in the Resources section. While on each website, check the return, replacement and warranty policies. It is also important to check the shipping policies; since most of these compressors cost a few hundred dollars each, you may find that some sellers will ship them for free. Be wary if a seller charges for shipping by weight, though, because many of these compressors are fairly heavy.
Check the shopping aggregator sites like Amazon one more time, and compare the prices you found at local shops, art supply sites and in the Amazon results. Make sure you factor shipping costs into your final cost analysis, then determine which seller is offering the best deal.
Purchase the compressor from your chosen seller. If you're buying online, you may need a major credit card to complete the purchase.