Not much help, but...
Peter White Cycles has them listed, but notes: "...Just a few left. Only available in a built wheel.". Note that his shop is closed through September 19th.
Saint Johns Street Cycles (out of England), has T519's listed. Not sure how much, or how secure shipping would be for just the rims.
Other shops that pop to mind which may be worth calling to check if they've a "stash" about include:
Ernies bike shops (Ohio)
Bens Bike (Wi)
Wheelworks (Ma)
Lastly, Sheldon Brown at Harris Cyclery (MA) might know where to get some, or be able to suggest alternatives for you (he is captain bike after all...).