Gunze has discontinued their acrylic Aqua line IIRC. The Mr Color lacquer line is still very much available, though, and IMHO the finest airbrushing hobby paints made when used with the leveling thinner. They're not hard to get at all as long as you don't mind getting them via mail (and live in the US... I've heard they're iffy to get into Canada due to being solvent based.)
Hobbywave has by far the best stock, price, and shipping of any vendor I've found yet as long as you're buying at least half a dozen paints or so. They're practically a Gunze storefront. They do a flat single rate ($12) for up to something like 50 bottles. If you're just buying one or two bottles the best way to do so in the US I've found (so far) is either SprueBrothers or Ebay. SB has very poor stock levels at any one time for Gunze stuff in general, though.
Pick out at least half a dozen paints you need, plus a bottle of leveling thinner, Surfacers / Dissolved putty if you need them, and Hobbywave will be the cheapest by far with the flat rate shipping. I wish they carried more than just Gunze stuff (like Tamiya kits and supplies) and I'd hardly ever buy from SB. That shipping deal is just too good to beat.