IslandRoast, Air Products is a nitrogen supplier that has a good network across the US. As for flushing a bag, it would depend on your packaging rate. If you pack on a weigh & fill, a cheap solution would be to rig up a 1/8" hose with a small regulator and shut off valve. Inserting the hose into the bag and applying the nitrogen for a few seconds will remove most of the oxygen before you then seal the bag. Nitrogen is a little lighter than air and air will creep back into an open bag if it is left out so it should be sealed quickly. Obviously this will slow your packaging rates and/or increase your labour.
Another alternative is to purchase a sealer with the nitrogen needle (similar to sealing with a vacuum needle). Packaging Aids has equipment such as this.
If you have a vertical form fill seal machine, a nitrogen delivery tube can run down the forming tube.
The final alternative is not to N2 flush, but to measure the oxygen levels in your bags 2 to 5 days after they're sealed. If you are packing freshly roasted coffee in 12oz valved bags (or bigger), the O2 content should have dropped to less than 3% in about 3 days as the degassing coffee does the flushing for you. If you're packing 2.5oz degassed ground coffee in a pillow pack, it is more difficult. The O2 levels will still drop as the coffee absorbs the oxygen, but this is due to the coffee staling. In pretty much all coffee bags, if the oxygen content is more than 10% 10-15 days after the bag was sealed, the oxygen barrier of the packaging material is not high enough or the bag is a leaker.
