I've been making a similar search during the past few days for some "instant" ground vehicles. At the airport I'm assisting with, the author is looking to have about 50% of the real-world vehicles there; that's 50% of the types available - so if the airport uses 4 types of pushback tug he will model the two most different ones, for visual variety - if I can't find models already available.
Drawings & blueprints ...
The problems with sizing etc can sometimes be resolved by going to the maufacturer's website, provided you can get the make from some of your source images. For example this particular airport uses Trepel trucks (usually on some other chassis but the body is Trepel), and with pushback vehicles the manufacturers at this particular airport are Douglas, Goldhofer, TLD and one other make (fortunately a boxy one that he can make using guesswork!). Now, the problem is that Trepel provide specifications for sizing but the pushback manufacturers don't! Similarly the fire/crash tenders sometimes give sizes but often don't. E.g. Sides (Renault) of France have lots of nice PDF brochures but nothing to help a hapless Gmax modeller from sizing the model properly, leading to a series of guesses that get refined over a few iterations. It is far nicer to know that your truck is x metres by y metres by z metres and get the basic box right first time.
However I've developed a method of trying to get to the facts, and in some cases it has worked okay. The problem is that sometimes it takes longer to reach a specification than it would have taken to guesstimate the size of the vehicle by trial & error in FS, so you have to always keep in mind how much time the search is taking. On the author's advice, I give a search for specifics about 30 minutes at most.
First priority is to try to get the manufacturers of the vehicles. It helps if you can make contact with a spotter, airport worker, or even a flightsimmer in the area who can legitimately look at these things. If you are told that the baggage cart tugs are made by Tiger, you can at least focus your searches a lot better and save a lot of time. You might still draw a blank, but its better to draw a blank after 2 days than 2 weeks. Knowing the make gets you over halfway there, the next thing is to get decent images. An airport worker *might* help you, but he or she would be risking their jobs if they did, in this febrile climate we have.
Some manufacturer websites look promising (eg Douglas) but provide only a limited number of specifications with measurements. Sometimes they compensate by providing decent side-on images, often they don't. Side-on is not dramatic or imposing, so they're normally views from one quarter or another, which is not ideal for getting shape and approximate size.
If you don't have any specifications or measurements, you might still have some pictures online that also have that 6-foot measuring stick known as a human being in the picture too. For vehicles, the margin of error if the person is an inch or so shy or high of 6' isn't as bad as if you were measuring a building! Actually, I treat the average person as being 5'11", which is near as dammit to 1.8 metres. I've been known to cut the image of a person in the picture and lay copies lengthwise on the ground to gauge the length of the truck he stood by. Desperate measures, but sometimes its not an exact science.
Also, bear in mind that vehicles with a common purpose often are very similar. The sizes for a Tiger tug will be broadly similar to its competitors.
Here's a list of the common ground-handling vehicles that shows what some searches can pull up.
http://www.sageparts.com/html/one_stop_shop.html
With a list of names, it makes the job very slightly easier, but obviously a list of names from someone at the airport would be even better!
If you don't mind making something generic (eg a baggage cart) you can just pick names from the list and see what you get. From that One-Stop-Shop list, if I choose Clyde machines for my baggage carts, I can just "Google" that name and find their website. Navigating to
http://www.clydemachines.com/prod07.htm I find a list of baggage cart dimensions that I can make generic carts from. Like I said, though, some manufacturers are hopeless for showing how large their vehicles are.
Also, having said all the above, here I am looking for readymade objects too (without much luck). I'm still hoping to find some philanthropic website where a scenery author has put low-poly ground vehicle models out for download. I'll probably find the Holy Grail first.
