I agree with Johnr, possibly the ITA would be your best bet for total truck registrations in a particular APR.

Although it doesnt cover LIFT TRUCKS a source that we use for prospecting is Selectory. This is an online data base that we can use to develope reports on companies or prospects by industry, SIC, # of employees, square footage etc. The data can be as specific as a zip code, municipality, or state, depending on how you want to slice it up

Puting together a combination of data from both of these sources may get you pretty close to what you are looking for, at least enough to make some pretty solid corolations, or trends