Hi
Any particular jets in mind?
There's a Canadian 3d Modeller http://www.milviz.com/ that makes some of the best detailed work I've seen. but they only have the Me 262.
they also sell all their models on TurboSquid although you can contact then directly to get other formats saved out - or even models comissioned.
One of their modellers has his own 3d artwork site - where some of his more unusual work is shown at http://www.airart3d.com/
Not sure if any is for sale though, His 3d Gallery part of the website has a Horten Ho18b , the odd Fw TreiFlugel, and in the "older" images
renderes of Ju EF.128, 132, 137, Messerschmitt Zerstörer I, Horten Ho 229B, Messerschmitt P.1110/I and other variants.
Other odd links you could try ( from his old site ) are:
http://www.angelfire.com/sk/gatial/
http://www.luft46.com/
http://digitalaviationart.com/skyraider3d/mep1070_1.htm
Back on Turbosquid theres a Junkers-EF132 om:
http://www.turbosquid.com/3d-models/3d-max-prototype-german-jet/348658
http://www.turbosquid.com/3d-models/maya-prototype-jet-fighter/348347
http://www.turbosquid.com/3d-models/3d-heinkel-jet-fighter/168182
http://www.turbosquid.com/Search/Artists/capun
http://www.turbosquid.com/FullPreview/Index.cfm/ID/168040
http://www.turbosquid.com/3d-models/3d-messerschmitt-fighter-model/233619
http://www.turbosquid.com/3d-models/maya-focke-wulf-triebflÜgel-fw/399862
http://www.turbosquid.com/3d-models/heinkel-162-volksjäger-people´s-max/399640
http://www.turbosquid.com/3d-models/3d-model-horten-ho229-1-german/399558
http://www.turbosquid.com/3d-models/3d-model-of-messerschmitt-163-b-komet/405252
http://www.turbosquid.com/3d-models/3ds-max-messerschmitt-163-s-komet/405253
and a free model:
http://www.turbosquid.com/3d-models/free-3ds-model-messerschmitt-me262a1-jet-fighter/168050
http://www.turbosquid.com/3d-models/arado-377-heinkel-3ds-free/258607
Hope some of these may help
Regards