You'll probably be better off trying to exchange them, either way it's going to cost $$
Air Gas on Capital carries them, or if you know someone who regularly has bottles exchanged, pay him for full current bottles and swap them out with him. ( sadly, I know no one well enough to do this for you in a timely manner )
i take my forklift tank to uhaul on capital, i told them the gauge leaked and they just exchanged it.
national welders are assholes(air gas) when i send my wife up there they won't even help her load a tank(i guess they don't want to assume any responsibility)
Otherwise, go by airgas during lunchtime when they have the resident dumbass working the counter and tell him you want to exchange a forklift tank. Ive never had them even look twice at all the shitty old various tanks i bring in, but we do have an account i guess.
The liquid forklift tank valves are not "out of date". That only applies to vapor valves, like in typical 20lb, 30lb, 40lb, etc. Your 33lb forklift cylinder does have to be recertified, but that basically consists of checking valves, leaks, guages, rust, foot ring, collar, and then stamping a new date on it. Most propane dealers should handle it no problem.
talked to a LP tank truck "operator" today, asked about the re-cert process, not much info but I did see him short fill 4 of 5 lift tanks, and watching how he was operating, I'm amazed there aren't more tank truck accidents, says a lot for the design of the equipment ( smarter than the operator )