As far as I know, there is no readily available, cheap test for lead particulate levels. The levels we'd be interested in are only a few ppm (parts per million), and that would be laboratory-quality stuff.
The military vehicle weapons toxic fumes testing I have supported were in the field, at military firing ranges. The chemical toxicity testing was done with dozens of clear vinyl lab-quality tubing (dozens of feet each) attached to air pumps and leading to a motorhome-sized mobile laboratory. After each firing scenario, several minutes were needed for the samplings to be taken, and many more minutes to purge the vehicle and prepare for the next scenario.
In the lab van, infrared absorption spectra and uv emission spectra were used to identify and quantify toxic hydrocarbon gases. These sampling methods simply are not available to most shooters.
I like the previous poster's vacuum cleaner method. It should be perfect for venting the smelly stuff while casting indoors.
Oh, by the way, most modern armoured vehicle turrets use a similar method to vent firing fumes from the crew spaces.
HTH
John :-)