You have three choices when it comes to finding a real game worn Cornell jersey. You can try to obtain one from the Teagle issue room, you can buy one on the game jersey open market or you can try to find one on eBay.
Acquiring a jersey from the Teagle issue room is actually quite a straight forward process with the proper information in hand. You need to contact William Reynolds (firstname.lastname@example.org) via email to let him know you are interested. You then simply need to stop by the issue room during the week between 10am and 4pm to pick up your jersey. The jerseys are $100 apiece and have had the name plates and captain's letters removed. Bring a numbered roster along if you have a specific palyer's jersey in mind. (Thanks to Mike Rosenberg '04 for this information.)
With regard to the secondary game worn jersey market, you essentially have to search the web site of each and every game worn jersey reseller. As many of these dealers primary business is in NHL jerseys, NCAA teams are frequently stuck in with the minor league or in other odd places. You can find a list of dealers at http://www.gameworn.net/dealers.html. While this should not be taken as an endorsement, people have had success in the past with Byron's Hockeyland and the Detriot Hockey Company. You can expect to pay about $125 to $150 plus tax and shipping.
Finally, you can always look on eBay for Cornell hockey related items.
You should also be aware that Perfect Screen Printing sells a "replica" Cornell jersey. However, if you look closely, you will notice that they are really Red Wings blanks with Cornell stitched on. How can you tell? The sleeves are red white red instead of white red white.