Yeah, I'm positive there are those that have some great discontinued stuff still in stock, but these things only be found through a) luck and timing or b) knowing the right people.
If you build yourself a solid relationship with a larger OPD account, they can take care of you. It'll prove invaluable as well when they introduce you to their reps or to other OPD owners. If you've got a good enough relationship, they'll give you a call when the rep's schedule to come by to show their samples, or they may invite you to the buyers showroom when they go (though this stuff is really boring). If corporate bigwigs are in town, they may call you up and you can come on down to meet them.
As for getting the older stuff, I find that OPDs in town know each other, so they can reach out to see if other accounts have anything (they can even get reps to check for you). In fact, some of my more difficult to obtain items were due to OPDs I know reaching out to someone he knew halfway across the country.
Like everything, it's all who you know.