Dendrimers are specially designed molecules that can carry a therapeutic substance to specific sites in the body because they will only attach to molecule sites they were designed for. It's a way of fine-tuning a drugs selection of attachable sites. For example, a normal chemotherapy drug will affect anything and everything in the body that will react with it in an indiscriminate manner, whereas when attached to a dendrimer it will only lock to malignant sites or cells.
You get access to them by being appropriately prescribed them, as determined by a medical professional.