Not really slicks but Schwalbe has two road tires in that size range that might be good, the Big Apple, size 50 x 559 and the Marathon Plus, size 47 x 559. The Marathon Plus is supposed to be about the most puncture resistant bike tire made.
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Gear Hubs Owned: Rohloff disc brake, SRAM iM9 disc brake, SRAM P5 freewheel, Sachs Torpedo 3 speed freewheel, NuVinci CVT, Shimano Alfine SG S-501, Sturmey Archer S5-2 Alloy. Other: 83 Colnago Super Record, Univega Via De Oro
Visit and join the Yahoo Geared Hub Bikes group for support and links.
http://groups.yahoo.com/group/Geared_hub_bikes/