I do all my buying and selling eBay, and there are still some few USAnians like myself who ship internationally. In fact, much of my sales are to countries where the US$dollar is weak. for which I am very happy. I will list some more lenses in the next few days -- not much good for Pentax, unfortunately. But I constantly see good lenses at what I consider good prices, and I am CHEAP.
What to look for: The best zooms are new autofocus glass from Pentax, Sigma, Tamron. The best prime (fixed focal length) lenses are old manual glass from Pentax, Zeiss, Vivitar, and others. The best mostly-inexpensive lenses bear those names, as well as Sears, Porst, Meyer, and others. Some good lenses made by Tokina, Tomioka, Kiron and others may carry names like Sears, Porst, Vivitar, Lentar, Hanimex or Hanimar, Focal, and others. Other quality brands include Ricoh, Petri, Yashica, Mamiya-Sekor, Fujica, etc.
BE AWARE that many of these brands use various mounts including Pentax. Most other mounts will NOT work easily on Pentax dSLRs. If you have any doubt about a lens, this is the place to ask questions. And be sure to check the
lens review databases here. Good luck!