A small Cryo compressor, a good started project for someone who wants to venture down this path. Low wattage, low price but should be fine to learn.
Or... Suck the gas out and use in a cascade. Several on ebay at this price. Polycold gas blend as awesome and very expensive.
http://www.ebay.com/itm/IGC-Polycold...item1e956a6c14
PDF:
http://instrumentation.obs.carnegies...G_Brochure.pdf
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