The first thing that comes to mind when one finds a store of unused nano-vac is "Its Pink!"
A moment is needed to stand back and acknowledge the ramifications of uncounted millions of tiny machines under command from outside swimming through your blood stream.
But noticing the color is easy. Unadulterated, the machines suspended in a saline solution would have the silvery appearance of mercury, with a bit of multi-colored iridescence from the way light is bouncing off thousands of tiny surfaces. However, having metallic sludge pumped into your arm would be a rather scary experience, and and such an opaque fluid could be adulterated with other elements (like actual Mercury) by the unscrupulous to con the unsuspecting. Thus in non-bulk form, a bubblegum pink dye is added to make it "friendlier" to the consumer.
Furthermore, the colorant indicates the viability of the machines. It breaks down under exposure to the same sorts of things that can ruin a batch of nano - high heat, UV, and intense radiation of the alpha, beta, X, and gamma variates. (Visible light, most types of radar, and EMP have are generally not a problem.) Provided the stuff isn't exposed to one of the above destructive energies, its inorganic and thus doesn't rot - allowing them to last almost forever.
Inside the body the useful life is generally quoted as fourteen to twenty months. It will actually work for several years longer than that, but each new injection introduces new upgrades and compensates for units lost through wear and accidental excretion. (While the body can't really notice the micro machines, they do get everywhere and thus can end up expelled in everyday occurrences like sweat)
Finding the stuff isn't too easy, as the obvious places - hospitals and mobile labs - have been looted already. Fortunately, the stuff is rather ubiquitous.
A good amount would be in transit at any given time, so all one has to do is find the right truck or shipping container. Given that this is a needle in a hay-stack approach - finding an old shipping manifest would be a great help - either check hospital inventories insurance agencies (both because they watch HMOs and insure the transit of such valuable materials) or a university to find one of those.
Government buildings or military bases might have a cache on hand for emergencies.
Technical or medical schools might have the means to produce more, though that is a big if. After all, its not like a bunch of tiny yellow robotic arms are putting together even tinier cars. Instead its a chemical process in a clean room - so you need power, know how, a hermetic environment, and the right precursors at the right time. Still, there may be a small supply on hand waiting to be shipped out.
Dosage varies by age and build, though its generally around 350mg/per kg (about 23 grams fro a 65kg/140lb individual) higher for children or elderly, and is administered in a fairly dilute form via IV over twenty to thirty minuets. In the barter economy a single dose is valued at over a week of labor, or a good weapon, a few dozen could acquire a vehicle if one is available. Of course, this is all highly dependant on what the community needs. There are in fact, those who won't accept the stuff since its one of the possible causes behind the reanimate phenomenon.