If I knew how to go about creating high quality parts that companies such as BrickForge are able to create, I wouldn't hesitate to take it upon myself to invest in the firefighter/ rescue market for tools and equipment. There are literally hundreds of enthusiasts who model fire engines and ambulances and recreate amazing scenes of fires, car accidents and other rescue incidents. These groups and individuals can be seen on MOCpages, flickr, specialized forums and groups on yahoo or even EmergencyBricks.com
Tools that seem like they'd be relatively easy and inexpensive to create but would yield high profit margins include:
Fire Dept Related:
halligan bars, nozzles, pike poles, denver tools, realistic ladders, jaws of life, extinguishers, assorted hand tools, air packs, customized fire helmets to make them a bit more realistic.
LifePack Cardiac Monitors, realistic stretchers/cots, iv bags, stethoscopes, oxygen tanks, "jump bags" and many more.
I am personally a firefighter and paramedic in real life and would be happy to act as an adviser to help narrow down what would be best suited to this niche community, most recognizable, and of course what would be simplest and most feasible to be created. That is, if you do decide to take a stab at what I believe is indeed a really good market to tap into.
(There are plenty of builders who have spent thousands just on their trucks, and there is a large post in many forums including my own talking about their desire to purchase custom firefighting gear if it was out there)