According to Colonization of Venus, by Geoffrey A. Landis (2003), most resources necessary for sustaining the colonies will be accessed in situ.
A permanent settlement will need access to the resources required for human life and for greenhouses to provide food and oxygen, and the atmosphere of Venus has these in abundance. Atmospheric carbon dioxide and nitrogen are a plentiful resource. Along with hydrogen reaped from condensing atmospheric sulfuric acid droplets, the basic elements needed for human survival can be found in the atmosphere.
A settlement will require structural and industrial materials as well. These materials, such as silicon, iron, aluminum, magnesium, calcium, potassium, sodium etc. can be mined from the surface material, which is apparently primarily a basaltic silicate. Access to the surface is relatively simple from an aerostat, since the thick atmosphere allows flight by airplanes (Landis 2001) or balloons (already demonstrated on Venus during the Russian VEGA mission [Bougher, Hunten and Phillips 1997]).
As Nick2253 points out in his comment below, the surface may be accessible enough, but conditions for mining are extremely challenging. Air pressure at the planet's surface is about 92 times that at Earth's surface, while temperatures run at least 462$^o$ C (864$^o$ F). Perhaps by the time such colonies exit the technology could be hardy enough, but it's a good bet many such materials will have to be imported.
With sufficient hydrogen and all that CO2, via the Sabatier reaction, comes methane, useful as fuel.
Breathing oxygen for life support can be easily provided by separation of oxygen from atmospheric carbon dioxide, either by zirconia electrolysis or by Sabatier processes.
Landis uses breathable air as part of his lifting support.
On Venus, breathable air (i.e., oxygen/nitrogen mixture at roughly 21:78 mixture ratio) is a lifting gas. The lifting power of breathable air in the carbon dioxide atmosphere of Venus is about half kg per cubic meter. Since air is a lifting gas on Venus: the entire lifting envelope of an aerostat can be breathable gas, allowing the full volume of the aerostat to be habitable volume. For comparison, on Earth, helium lifts about one kg per cubic meter, so a given volume of air on Venus will lift about half as much as the same
volume of helium will lift on Earth.).
I can imagine it as living in a bubble with a partially dirt deck where the tomatoes grow.
I don't think it's speculation that cargo ships with supplies of LOX, cargo containers of ice, and the mail, among other things, would spring up to service such floating Venusian colonies. The logical infrastructure (to my mind) would be "space supertankers" that are captured into low Venus orbit, serviced by optimized craft designed to ferry goods from orbit to aerostat.