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UV lenses are so expensive and rare because very few of them were made. Very few were made because the optical elements were made of fluorite instead of optical glass. Your best bet to find a "reasonably" priced UV lens is to contact Edmund Scientific. They are currently in the business of supplying technical optics and are likely the only source. Edmund Scientific is on the Internet and you can find their site with a quick search. Other then this source the only UV lenses I know of are the ones you have mentioned.