You can. Every once in a while some show up for sale in the states. One place to keep track of is www.sor.com and check out the used vehicle place. You can also buy in Canada and import. Just kind of some work to get all the importation and all that done. You need to find a RI (registered importer) that knows that you can import BJ 70s to the states. There was one in sor.com classifieds in Canada that has a "new" rust free Japanese body on it. Would be a good deal for someone.
Just a thought on your desire for a diesel pickup. Find a 85 vintage toyota pickup with the little 2LT diesel engine and I know someone that you can get a low milage engine for to swap it with. I think these only came in regular cab though, but came stock with the solid front axle still I may go this route in the future.