The season 3 finale was last night. They ran every episode of the series last week leading up to the finale. Unless you want to buy a season pass from Amazon or iTunes your best bet is to keep checking out the guide and hope they do another marathon.
If you don't want to wait for a marathon or the Blu-ray release in October. iTunes has the season pass available right now in HD for $42.99. Amazon Instant also has it available right now. The SD season pass on amazon is $30.25 or they have it in HD for $45.45. The choice really depends on which streaming device you are using.
I know that is a pretty hefty price tag but this show has had me hooked since the first episode. I know I couldn't wait till the disks are released in October if I hadn't seen it yet. Netflix seems to get the Walking Dead seasons available on instant a month or two after the disks release. Last year we ended up buying the Season 2 pass on iTunes even though I had already seen it when it aired because another family member got hooked. We tried to wait for a marathon for a while but found that AMC didn't show repeat episodes of this show much when it was out of season.
Since this thread already exists...did anyone else notice a persistent image stuttering in the last few episodes of the Walking Dead? It seemed to occur maybe every 30 seconds or less, like a frame or two was dropped.
I would blame my provider (currently uverse), except I haven't noticed the issue during any other AMC broadcast.