Monoclonal antibodies are just antibodies that are monospecific (ie they bind one target really well). And it looks like there a number of drugs under this category (anything ending in -mab usually) are in stage II/III of clinical trials (meaning they are likely to be approved in the coming years).

What you mention about cell division rates being slow was solved by the hybridoma protocol where you fuse two cells, one of which is a myeloma (cancer that is a rapidly reproducing cell line) and another is a B cell that produces Antibodies that are specific for your intended target. Since then there have been a lot of strides in monoclonal antibody production. [https://en.wikipedia.org/wiki/Monoclonal_antibody#Production]