Look at the 5th picture of this forklift on E Bay, item # 110669807669. Zoom in and you will see the stop. They also use welded on ones that would be located just behind, and up and over the channel the fork clips on to hold it.
Don't worry about what dealer sold this unit original or even the second or third time. You know the brand you bought. Go to the Yellow pages & find the closest dealer to you that is an authorized dealer - contact them. No doubt they will ask you the Model Number & Truck serial number. This information is on the truck data (aka name plate) unless it has been removed.
GL
If you look at the end of the carriage where the forks mount you may see threaded holes. Typically you would inert a bolt in the hole, with a plate/stop protruding forward to stop the forks sliding off fo the end of the carriage. All lists are different, and thus it's hard to give a more specific answer
I guess maybe this lift originally was bought from another dealer since I am not able to get any info from them. I got it at an auction so don't know where it was originally purchased. I'm really not concerned about the load backrest though because it won't ever be lifted that high or that anything will fall. I really just need to know where to look for the stop you refer to on the carriage bar. Would that stop be easy to see to know if one is there or not and do I need to look in more than one place? I'm sure I could pull the fork over to see if anything stops it but really don't want to take a chance of it coming off.
Do you have any photos or suggestions where I can see what I should be looking for. And if I don't find anything like that on this forklift, what would you do to make sure the forks couldn't come off?
Some manufacturers will weld a stop on to the ends of the upper carriage bar or other have a pre-drilled hole in the face of the carriage into which a bolt is inserted to act as a stop. But OSHA requires any modification to equipment be approved by the manufacturer. You need to discuss this with the local dealer for the brand of forklift you have.
The OSHA requirements for a load back rest is if the load can be lifted above the operators head and there is the possibility the load or parts of the load can fall backwards towards the operator (like when back tilting or driving up a grade) a load backrest shall be fitted to the forklift.
A few manufacturers will approve removal of the LBR if the get a letter of indemnification from the owner & some won't (especially if the forks can travel above the operator's head). The only time I've every see one issued is when the lift was fitted with a "truckers special" mast - max lift height 78" or if the lift trucks was to be fitted with an attachment, like a rotator, carton clamp or rotating paper roll clamp.