One of the things I quickly learned when I started looking around for lumber to build my SOF & wood stripper was that tracking down who carried different species of wood took some time. Forget the big box stores for western red cedar, redwood or BB. Local lumber yards around my area (Louisville Metro) carried WRC & redwood as well as marine ply which I was ready to use until I talked to a friend of a friend who worked in veneer and told me to check out one of their suppliers, Hood Distribution. Sure enough, they had 1/2"x 5x5 BB for $35 a sheet. Took a few weeks to find it, but with due diligence it can be found. Hood Dist. is located mostly in the southeast. I would think in other parts of the country there would be similar companies. Finding suppliers for this & that is just part of the building process.
If you decide to construct your own float bags out of vinyl, check your local fabric store, but for the HH-66 vinyl cement I could only find that online.
Happy Building.