Its possible to get tickets, but the price will be very high!

Ebay is a good source but BEWARE of scammers anytime you buy tickets.. I would also use Paypal.. I always search Ebay for local sellers who will let me pick the tickets up in person .. Another source is stubhub.com.. They are usually fans selling to fans .. Prices will very , if the packers are doing well expect to pay more for them.. Also if you buy them early , before the season starts you can usually find a better deal ..

stubhub.com
or
ebay.com

are two decent routes

Packer games are hard- u almost gotta know someone because they are owned by the fans, which means most of the seats belong to season ticket holders- especially end zone tickets!